NCERT Solutions for Class 11 Physics Chapter 5 Laws Of Motion

NCERT Solutions for Class 11 Physics Chapter 5 Laws Of Motion

Edited By Vishal kumar | Updated on Aug 25, 2023 11:52 AM IST

NCERT Solutions for Class 11 Physics Chapter 5 Laws Of Motion is a very important resource to score well in exams. On this page you will get the complete in detail and step by step from question number 5.1 to 5.23 (Exercise solution) and question number 5.24 to 5.40 (additional exercise). These class 11 physics ch 5 NCERT solutions are created by subject matter experts of careers360 according to the latest NCERT Syllabus 2023 - 24. Students can also download the class 11 physics chapter 5 exercise solutions in the form of a PDF and use it according to their comfort anytime anywhere without any charge or technical glitch.

The applications of formulas studied in the NCERT chapter 5 Laws of motion can be well understood with the help of a tool like Laws of Motion Class 11 NCERT solutions. Consider the situation in which you are travelling on a bus. The bus is moving in a forward direction and suddenly the bus applies the brake. Now definitely you will move in the forward direction. This is due to the law of inertia of motion. The concept of inertia is well explained in Class 11 Physics chapter 5 Laws of Motion. This chapter Laws of Motion deals with the physical and numerical aspects of Newton's laws of motion.

Now consider the situation in a football moving on the ground stops after some time. The ball stops because of an external force acting on the ball against its motion. This force is the frictional force. Now imagine the case where friction is absent. Whether the ball stop? That is unless an external force is applied to a body it continues its state of uniform motion along a straight line or continues its state of rest, this is explained by Newton's first law of motion which we studied in chapter 5 physics class 11. NCERT solutions help you to check your knowledge about what is studied in the Laws of Motion Class 11 chapter. There are many numerical problems explained in the NCERT.

**According to the CBSE Syllabus for the academic year 2023-24, the chapter you previously referred to as Chapter 5, "Laws of Motion," has been renumbered as Chapter 4.

NCERT Class 11 Physics Chapter 5 Exercise Solutions

Q5.1 (a) Give the magnitude and direction of the net force acting on

Since the drop is falling with constant speed, so the net acceleration of the drop is zero. This means net force on the drop is zero.

Since the cork is floating on the water, that implies the gravitational force of cork is balanced by the buoyant force. Thus net force acting on cork is zero.

Since the kite is stationary in the sky, thus according to Newton's law, the net force on the kite is zero.

Since the car is moving with constant velocity thus the net acceleration of the car is zero. Thus net force acting on the car is zero.

Q5.1 (e) Give the magnitude and direction of the net force acting on

Since the electron is free from the electric and magnetic field so net force acting on the electron is zero.

(a) during its upward motion

During upward motion, the force acting on the pebble is only the gravitational force which is acting in a downward direction .

The gravitational force :

=mg

or =0.05(10)N

or =0.5N

(b) during its downward motion,

Since the pebble is moving in the downward direction the net force acting is also in the downward direction .

The net force is the gravitational force.

Gravitational force:-

=mg

or =0.(05)10

=0.5N

(c) at the highest point where it is momentarily at rest. Do your answers change if the pebble was thrown at an angle of 45° with the horizontal direction? Ignore air resistance.

At the highest point velocity becomes zero for a moment. At this point also, the net force acting is the gravitational force which acts in the downward direction .

Gravitational force:-

$=\ mg$

or $=\ (0.05)10$

$=\ 0.5\ N$

When a pebble is thrown at 45 0 with the horizontal direction then also net force will be the same gravitational force.

Q5.3 (a) Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg,

Since the train is stationary so the net force acting on the stone is the gravitational force which acts in the downward direction .

Gravitational force :

$F\ =\ ma\ =\ mg$

or $=\ (0.1)10$

or $=\ 1\ N$

Q5.3 (b) Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg

Since the train is travelling with the constant speed so the acceleration of the train is zero. Thus there is no force on stone due to train.

The net force acting on the stone will be the gravitational force which acts in a downward direction.

Gravitational force:-

$F\ =\ mg$

or $=\ (0.1)10\ N$

or $=\ 1\ N$

Just after the stone is dropped, the stone is free from the acceleration of the train. Thus the force acting on the stone will be just the gravitational force which acts in the downward direction.

The gravitational force is given by:-

$F\ =\ mg$

or $=\ (0.1)10$

or $=\ 1\ N$

Q5.3 (d) Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg,

As the stone is in contact with the train thus the acceleration of stone is the same as that of train i.e. 1 m/s 2 .

Thus force acting on the stone is given by :

$F\ =\ ma$

or $=\ 0.1\times 1\ =\ 0.1\ N$

This force is acting in the horizontal direction.

(i) $T$

(ii) $T - \frac{mv^2}{l}$

(iii) $T + \frac{mv^2}{l}$

(iv) 0

$T$ is the tension in the string. [Choose the correct alternative].

When the particle is moving in a circular path, the centripetal force will be :

$F_c\ =\ \frac{mv^2}{r}$

This centripetal force will be balanced by the tension in the string.

So, the net force acting is :

$F\ =\ T\ =\ \frac{mv^2}{r}$

We are given the retarding force. So we can find the deacceleration this force is causing.

By Newton's second law of motion, we get :

$F\ =\ ma$

or $-50\ =\ (20)a$

or $a\ =\ \frac{50}{20}\ =\ - 2.5\ m/s^2$

Now we will use the first equation of motion,

$v\ =\ u\ +\ at$

The final velocity, in this case, will be zero (Since the vehicle stops).

$0\ =\ 15\ +\ (-2.5)t$

Thus $t\ =\ \frac{15}{2.5}\ =\ 6\ s$

Thus the time taken to stop the vehicle is 6 sec.

Since the velocity of the body is increased by applying the force. This is possible only when the force is applied in the direction of the motion.

For finding the magnitude of the force, we need to calculate acceleration.

By using first equation of the motion,

$v\ =\ u\ +\ at$

or $3.5\ =\ 2\ +\ a(25)$

or $a\ =\ \frac{3.5-2}{25}\ =\ 0.06\ m/s^2$

Thus force can be written as :

$F\ =\ ma$

$=\ 3\times 0.06$

$=\ 0.18\ N$

The magnitude of the resulting force can be found by :

$R\ =\ \sqrt{F_1^2\ +\ F_2^2 }$

or $=\ \sqrt{8^2\ +\ 6^2 }$

or $=\ 10\ N$

Now force direction,

$\tan \Theta \ =\ \frac{6}{8}$

or $\Theta \ =\ 37^{\circ}$

The acceleration of the body is given by :

$a\ =\ \frac{F}{m}$

or $a\ =\ \frac{10}{5}\ =\ 2\ m/s^2$

Hence acceleration of the body is $2\ m/s^2$ and its direction is the same as of the resultant force.

Total mass of the system = 400 + 65 = 425 kg

Using first law of motion, we get

$v\ =\ u\ +\ at$

Since the car comes to rest, thus final velocity will be zero.

$0\ =\ 10\ +\ a(4)$

or

$a\ =\ \frac{-10}{4}\ =\ -2.5\ m/s^2$

So the force required :

$F\ =\ ma$

or $=\ 465\times (-2.5)$

or $F\ =\ -1162.5\ N$

So the magnitude of the force is 1162.5 N and it is retarding force.

Let the initial thrust be F Newton.

Using Newton's second law of motion, we get

$F\ -\ mg\ =\ ma$

or $F\ =\ ma\ +\ mg$

$F\ =\ m(a+g)\ N$

Substituting values in this equation, we get :

$F\ =\ 20000(5+10)$

or $F\ =\ 3\times 10^5\ N$

The acceleration of force is given by :

$a\ =\ \frac{F}{m}$

$a\ =\ \frac{-\ 8}{0.4}\ =-\ 20\ m/s^2$

At t = - 5 s :

There is no force acting so acceleration is zero and u = 10 m/s

$s\ =\ ut\ +\ \frac{1}{2}at^2$

or $=\ 10(-5)\ +\ \frac{1}{2}.0.t^2$

or $=\ - \ 50\ m$

At t = 25 s :

Acceleration is - 20 m/s 2 and u = 10 m/s

$s\ =\ ut\ +\ \frac{1}{2}at^2$

or $=\ 10(25)\ +\ \frac{1}{2}(-20)25^2$

or $=\ -\ 6000\ m$

At t = 100 s

We have acceleration for first 30 sec, and then it will move with constant speed.

So for 0 < t < 30 :

$s\ =\ ut\ +\ \frac{1}{2}at^2$

or $=\ 10(30)\ +\ \frac{1}{2}(-20)30^2$

or $=\ -\ 8700\ m$

Now for t > 30 s :

We need to calculate velocity at t = 30 sec which will be used as the initial velocity for 30 < t < 100.

$v\ =\ u\ +\ at$

or $=\ 10\ +\ (-20)30\ =\ -\ 590\ m/s$

Now $s\ =\ vt\ +\ \frac{1}{2}at^2$

or $=\ (-590)70\ +\ \frac{1}{2}.0.t^2$

or $=\ -\ 41300\ m$

Hence total displacement is : - 8700 + (- 41300 ) = - 50000 m.

The initial velocity of the truck is given as zero.

We need to find the final velocity (at t = 10 s), so we will use the equation of motion :

$v\ =\ u\ +\ at$

or $=\ 0\ +\ (2)10\ =\ 20\ m/s$

This is the velocity imparted to stone by the truck that's why it is a horizontal component of velocity.

The stone is dropped at t = 10 sec. so it has travelled 1 sec in the air (11 - 10 = 1 s). We need to find the final vertical velocity.

$v\ =\ u\ +\ at$

$=\ 0\ +\ 10(1)\ =\ 10\ m/s$

Thus resultant of both the component is the required velocity.

$R\ =\ \sqrt{v_h^2\ +\ v_v^2}$

or $=\ \sqrt{20^2\ +\ 10^2}$

or $=\ 22.36\ m/s$

Direction :

$\tan \Theta \ =\ \frac{v_v}{v_h}\ =\ \frac{10}{20}$

or $\Theta \ =\ 26.57^{\circ}$

When the stone is dropped, the stone comes only in effect of gravity.

So the acceleration of stone is 10 m/s 2 and it acts in the downward direction.

At the extreme positions, the velocity of the bob will become zero for a moment. So if we cut the string at this time, then Bob will fall vertically downward due to gravity.

At the mean position, the bob will have velocity tangential to the circular path (it will be completely horizontal). If the bob is cut at this place then it will follow a parabolic path having only horizontal velocity.

(a) upwards with a uniform speed of 10 m s -1

What would be the readings on the scale in each case?

Since lift is moving with a constant speed or in this case constant velocity so the acceleration provided to man by lift is zero.

The net force on the man will be zero. So a = 0.

Using Newton's law of motion, we can write :

$R\ -\ mg\ =\ ma$

or $R\ -\ mg\ =\ 0$

Thus $R\ =\ mg$

$=\ 70\times10\ =\ 700\ N$

So, reading on weighing scale will be :

$=\ \frac{R}{g}\ =\ \frac{700}{10}\ =\ 70\ Kg$

(b) downwards with a uniform acceleration of $5ms^{-2}$ .

What would be the readings on the scale in each case?

(b) Using Newton&##39;s law of motion, we have :

$R\ +\ mg\ =\ ma$

or $R\ -\ 70(10)\ =\ 70(-5)$ (Since we took downward direction as negative and upward as positive).

or $R\ =\ 700\ -\ 350\ =\ 350\ N$

Thus the reading on the weighing scale will be :

$=\ \frac{R}{g}\ =\ \frac{350}{10}\ =\ 35\ Kg$

(c) upwards with a uniform acceleration of $5 ms^{-2}$ . What would be the readings on the scale in each case?

(c) The acceleration of lift is given to be 5 m/s 2 . Let us assume the upward direction to be positive.

Using Newton's law of motion, we can write :

$R\ -\ mg\ =\ ma$

or $R\ -\ 70(10)\ =\ 70(5)$

or $R\ =\ 350 +\ 700\ =\ 1050\ N$

Thus the reading of the weighing scale will be :

$=\ \frac{R}{g}\ =\ \frac{1050}{10}\ =\ 105\ Kg$

(d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

(d) If the lift falls freely then the acceleration of lift will be acceleration due to gravity.

Using Newton's law of motion we can write :

$R\ -\ mg\ =\ ma$

or $R\ -\ mg\ =\ m(-g)$

or $R\ =\ m(-g)\ +\ mg\ =\ 0\ N$

Thus the reading of weighing scale will also be zero since there is no normal force.

This state is called the state of weightlessness.

(i) For t < 0 :

In this range the position of particle coincides with time, that implies no motion takes place. Hence net force on the particle is zero.

(ii) For t > 4 :

In this range displacement of the particle is not changed so the net force is zero.

(iii) For 0 < t < 4 :

In this range the slope of the position-time graph is constant that means the particle is moving with constant speed. And hence net force, in this case, is zero.

(b) impulse at t = 0 and t = 4 s ? (Consider one-dimensional motion only).

Impulse is defined by :

$I\ =\ mv\ -\ mu$ (Change in momentum).

At t = 0 s :

$u\ =\ 0\ and\ v\ =\ \frac{3}{4}\ m/s$

or $I\ =\ 4(\frac{3}{4})\ -\ 0$

or $I\ =\ 3\ Kg\ m/s$

At t = 4 s :

$u\ =\ \frac{3}{4}\ m/s$ and $\ v\ =\ 0$

Thus $I\ =\ 0\ -\ 4\left ( \frac{3}{4} \right )$

or $I\ =\ -3\ Kg\ m/s$

We will consider A and B in a system. So total mass in the system is = 10 + 20 = 30 Kg.

Thus acceleration of the system is given by :

$a\ =\ \frac{F}{m}$

or $=\ \frac{600}{30}\ =\ 20\ m/s^2$

When force is applied at block A :

Using Newton's law of motion :

$F\ -\ T\ =\ m_1a$

or $600\ -\ T\ =\ 10\times20$

Thus $T\ =\ 400\ N$

We will consider A and B in a system. So total mass in the system is = 10 + 20 = 30 Kg.

Thus acceleration of the system is given by :

$a\ =\ \frac{F}{m}$

or $=\ \frac{600}{30}\ =\ 20\ m/s^2$

When force is applied at block B :

Using Newton's law of motion, we can write

$F\ -\ T\ =\ m_2a$

or $600 -\ T\ =\ 20(20)$

Thus $T\ =\ 200\ N$

Since both the masses are connected with string so they will have the same acceleration, let say 'a'.

We will apply Newton's law for each block individually.

For smaller block (8 Kg) :

$T\ -\ m_sg\ =\ m_sa$ ...................................................(i)

For larger block (12 Kg) :

The equation of motion is given by :

$m_lg\ -\ T\ =\ m_la$ ......................................................(ii)

Adding both the equations we get :

The acceleration is given by :

$a\ =\ \left ( \frac{m_l\ -\ m_s}{m_l\ +\ m_s} \right )g$

or $=\ \left ( \frac{12\ -\ 8}{12\ +\ 8} \right )10$

or $=\ 2\ m/s^2$

Now put the value of acceleration in any of the equations to get the value of T.

$T\ =\ \left ( m_l\ -\ \frac{m_l^2\ -\ m_s m_l}{m_s\ +\ m_l} \right )g$

or $=\ \left ( \frac{2m_s m_l}{m_s\ +\ m_l} \right )g$

or $=\ \left ( \frac{2\times 12\times 8}{12\ +\ 8} \right )10$

$=\ 96\ N$

Thus the tension in the string is 96 N.

Let the mass of parent nuclei be m.

And the mass of daughter nuclei be m 1 and m 2 .

Initial momentum is zero since the nuclei is at rest.

But after dissociation, the momentum becomes :

$M\ =\ m_1\ v_1\ +\ m_2 v_2$

Using conservation of momentum,

$0\ =\ m_1\ v_1\ +\ m_2 v_2$

or $v_1\ =\ \frac{-m_2 v_2}{m_1}$

Thus both velocities have opposite direction.

Impulse imparted can be calculated by knowing the change in momentum.

The initial momentum of each ball is :

$p_i\ =\ mu\ =\ (0.05) 6\ =\ 0.3\ Kg\ m/s$

The final momentum is given by :

$p_f\ =\ mv\ =\ (0.05) (-6)\ =\ -\ 0.3\ Kg\ m/s$

So the impulse is :

$I\ =\ p_f\ -\ p_i$

or $=\ -0.3\ -\ 0.3$

or $=\ -0.6\ Kg\ m/s$

In this question, we will use the conservation of momentum.

Final momentum = Initial momentum

For initial momentum :

Both gun and shell are at rest initially so momentum is zero.

For final momentum :

The direction of the velocity of the shell is opposite to that of the gun.

So, $p_f\ =\ m_s v_s\ -\ m_g V_g$

The recoil speed of the gun :

$V_g\ =\ \frac{m_s v_s}{m_g}$

or $V_g\ =\ \frac{0.020\times 80}{100\times 1000}\ =\ 0.016\ m/s$

The situation is shown below :

The horizontal components of velocity are to be considered for imparting impulse as vertical components are in the same direction thus impulse in the vertical direction is zero.

The impulse is given by a change in momentum.

Initial momentum = $-mv \cos \Theta$

Final momentum = $mv \cos \Theta$

Thus impulse is $=\ mv \cos \Theta\ -\ (-\ mv \cos \Theta)\ =\ 2mv \cos \Theta$

or $=\ 2\times0.15 \times15\ \cos 22.5 ^{\circ}$

or $=\ 4.16\ Kg\ m/s$

We are given, frequency :

$n\ =\ \frac{40}{60}\ =\ \frac{2}{3}$

So, the angular velocity becomes :

$\omega \ =\ 2\Pi n$

By Newton's law of motion, we can write :

$T\ =\ F_{centripetal }$

or $=\ \frac{mv^2}{r}\ =\ mw^2r$

or $=\ (0.25)\left ( 2\times\Pi \times \frac{2}{3} \right )^2(1.5)$

or $=\ 6.57\ N$

Now, we are given maximum tension and we need to find maximum velocity for that :

$T_{max}\ =\ \frac{mv_{max}^2}{r}$

Thus, $v_{max}\ =\ \sqrt{\frac{T_{max}.r}{m}}$

or $=\ \sqrt{\frac{200\times 1.5}{0.25}}$

or $=\ 34.64\ m/s$

(a) the stone moves radially outwards,

The stone should move in the direction of velocity at that instant. Since velocity is tangential at that moment so the stone will not move radially outward.

(b) the stone flies off tangentially from the instant the string breaks,

(b) This statement is correct as the direction of velocity at the instant of the breaking of the string is tangential thus stone will move tangentially.

(c) the stone flies off at an angle with the tangent whose magnitude depends on the speed of the particle?

The direction of velocity at the instant of breakage of the string is tangential so the stone will fly tangentially. Hence given statement is false.

Q5.23 (a) Explain why

The horse moves forward by pushing ground backwards. The ground will then give the normal force to the horse (action-reaction pair), which is responsible for the movement of the horse. In an empty space, no such force is present so the horse cannot get the push to run forward. Thus, a horse cannot pull a cart and run in empty space.

Q5.23 (b) Explain why

This is because of inertia. When the bus is moving our body has the same speed. But when the bus comes to rest, the inertia of our body opposes to stop and continues its motion. That's why passengers are thrown forward from their seats when a speeding bus stops suddenly.

Q5.23 (c) Explain why

Because when you pull the lawnmower at some angle, one component of force is in the upward direction and one in horizontal (to move). The vertical force reduces the effective weight of the motor which makes it easier. But in case of a push, the vertical force is directed downward which makes its effective weight even greater than before. That's why it is said 'pull is easier than push'.

Q5.23 (d) Explain why

According to Newton's law, we can write :

$F\ =\ ma$

or $F\ =\ m\frac{dv}{dt}$

Thus $F\ \propto \frac{dv}{dt}$

It can be seen from the equation that if we increase the impact time then the experienced force will be lesser.

So a cricketer increases the impact time by taking his hands backwards while holding a catch, resulting in less force on their hand.

Laws of Motion Class 11 Numericals With Solutions - Additional Exercise

From the graph, it is clear that the direction of motion is changing after every 2 seconds. And has the same magnitude after 2 seconds.

This can be understood from a situation that a ball collides with wall elastically in seconds and returns to the original mean position after 4 seconds.

Since the slope of the graph is changing after every 2 s, so impulse is given after 2 sec. of duration.

Velocity can be known by calculating the slope of the position-time curve.

$u\ =\ \frac{(2-0)}{2-0}\times 10^{-2}\ =\ 10^{-2}\ m/s$

or $v\ =\ -\ 10^{-2}\ m/s$

Therefore, the magnitude of impulse is given by = | Change in momentum |

$I\ =\ |mv\ -\ mu|$

or $=\ 0.04(-\ 10^{-2}\ -\ 10^{-2})$

or $=\ 0.08\ \times 10^{-2}\ Kg\ m/s$

The net force on the man is given by :

$F\ =\ ma$

or $=\ 65\times 1\ =\ 65\ N$

The maximum force can be exerted is given by :

$F_r\ =\ \mu mg$

or $=\ 0.20(650)\ =\ 130\ N$

So the maximum acceleration is :

$ma_{max}\ =\ \mu mg$

or $a_{max}\ =\ \mu g$

or $a_{max}\ =\ 0.2\times 10\ =\ 2\ m/s^2$

Lowest Point Highest Point

(a) $mg - T_1$ $mg + T_2$

(b) $mg + T_1$ $mg - T_2$

(c) $mg + T_1 - (mv_1^2))/R$ $mg - T_2 + (mv_1^2))/R$

(d) $mg - T_1 - (mv_1^2))/R$ $mg + T_2 + (mv_1^2))/R$

$T_1$ and $v_1$ denote the tension and speed at the lowest point. $T_2$ and $v_2$ denote corresponding values at the highest point.

The FBD of stone at the lowest point is shown below :

Using Newton's law of motion,

The FBD of stone at the highest point is given below :

Using Newton's law of motion we have :

Thus option (a) is correct.

(a) force on the floor by the crew and passengers,

(a) The normal force on the floor will be the reaction force due to crew and passengers.

Using Newton's laws of motion we can write :

$N\ -\ m_cg\ =\ m_ca$

Thus $N\ =\ m_ca\ +\ m_cg$

or $=\ 300\left ( 15\ +\ 10 \right )$

or $=\ 7500\ N$

The direction of normal force on the floor will be vertically upward.

(b) action of the rotor of the helicopter on the surrounding air,

(b) In this case, we need to consider helicopter and passengers in a system because we need to determine the action of the rotor.

So by Newton's laws motion, we have :

$R\ -\ mg\ =\ ma$

or $R\ =\ ma\ +\ mg$

or $=\ 1300\left ( 15+10 \right )$

or $=\ 32500\ N$

The direction of the force of rotor on the surrounding will be in the downward direction.

(c) force on the helicopter due to the surrounding air.

$R\ -\ mg\ =\ ma$

or $R\ =\ ma\ +\ mg$

or $=\ 1300\left ( 15+10 \right )$

or $=\ 32500\ N$

The direction of the force of the rotor on the surrounding will be in the downward direction.

By action-reaction pair, the force on helicopter due to the surrounding is 32500 N and it is directed vertically upward.

Firstly we will calculate the mass of water passing through per second :

$m\ =\ \rho V$

or $=\ \rho Av$

or $=\ 10^3\times15\times10^{-2}\ =\ 150\ Kg/s$

Force is defined as the rate of change of momentum.

$F\ =\ \frac{\Delta P}{\Delta t}$

or $=\ \frac{mv}{ t}$

or $=\ 150\times15\ =\ 2250\ N$

Q5.29 (a) Ten one-rupee coins are put on top of each other on a table. Each coin has a mass m. Give the magnitude and direction of
(a) the force on the 7 th coin (counted from the bottom) due to all the coins on its top.

The weight on the 7th coin is due to the top 3 coins.

So required force is equal to the weight of 3 coins = 3 mg

This force is acting vertically downward.

(b) the force on the 7 th coin by the eighth coin,

The eighth coin is placed directly above the 7th coin. Thus the net force experienced by 7th coin is due to 8th coin (as the 7th coin is in contact with 8th coin only from the top). Hence the force on the 7 th coin by the eighth coin is 3 mg.

(c) the reaction of the 6 th coin on the 7 th coin.

Since the 6th coin will experience a force due to 4 coins that are present above i.e., 4 mg. According to Newton's law of action-reaction pair, the 6th coin will have a reaction force on 7th coin of magnitude 4 mg in the upward direction.

Convert speed of aircraft in SI units :

$V\ =\ 720\ Km/h\ =\ 720\times\frac{5}{18}\ =\ 200\ m/s$

We are familiar with the following relation :

$\tan \Theta \ =\ \frac{v^2}{rg}$

or $r\ =\ \frac{v^2}{g \tan \Theta}$

or $=\ \frac{200^2}{10\times \tan 15^{\circ}}$

or $=\ 14925.37\ m\ =\ 14.9\ Km$

The required centripetal force is provided by the rails , as by Newton's third law of motion, wheels apply force on the rails and thus rails provides a force on the wheels (action-reaction pair).

We know that the angle of banking is given by :

$\tan \Theta \ =\ \frac{v^2}{rg}$

or $=\ \frac{15^2}{30\times10}$

or $=\ 0.75$

Thus $\Theta \ =\ 36.87^{\circ}$

Using Newton's law force applied on the block:- $F\ =\ ma$

or $F\ =\ 25\times10\ =\ 250\ N$

Weight of man = 500 N

Case 1:- When a man is lifting block directly, man is applying force in the upward direction directly.
The net force on floor : - 250 + 500 = 750 N

Case 2:- When a man is lifting block through pulley :

The net force on floor :- 500 - 250 = 250 N

Now it is given that the floor can yield 700 N of the normal force. Thus the man should adopt case 2.

(a) climbs up with an acceleration of 6 m s -2
(b) climbs down with an acceleration of 4 m s -2
(c) climbs up with a uniform speed of 5 m s -1
(d) falls down the rope nearly freely under gravity?
(Ignore the mass of the rope).

Given that T max = 600 N.

(a) Acceleration of 6 m s -2 in the upward direction:-

Using Newton's law of motion we can write :

$T\ -\ mg\ =\ ma$

or $T\ =\ 40(6+10)\ =\ 640\ N$

Thus rope will break.

(b) Acceleration of 4 m s -2 in a downward direction:-

Using Newton's law of motion we can write :

$T\ -\ mg\ =\ ma$

or $T\ =\ 40 (10-4)\ =\ 240\ N$

Thus the rope will not break.

(c) Upward with a constant speed of 5 m/s:-

Since speed is constant thus acceleration is 0.

$T\ -\ mg\ =\ ma$

or $T\ =\ 40 (0+10)\ =\ 400\ N$

Thus the rope will not break.

(d) Acceleration is due to gravity (in a downward direction):-

Using Newton's law :

$T\ -\ mg\ =\ ma$

or $T\ =\ 40 (-10+10)\ =\ 0\ N$

Thus the rope will not break.

The applied force is 200 N.

The maximum friction force on the system is given by :

$F\ =\ \mu \left ( m_A\ +\ m_B \right )g$

or $=\ 0.15 \left ( 5\ +\ 10 \right )g$ $=\ 22.5\ N$

So the net force on partition is 200 - 22.5 = 177.5 N.

This will be equal to the reaction of the partition (action-reaction pair). The direction will be leftward.

Consider block A.

The frictional force on block A will be :

$f_A\ =\ \mu m_Ag$

or $=\ 0.15\times5\times 10\ =\ 7.5\ N$

Thus net force on B due to block A is = 200 - 7.5 = 192.5 N.

The net force on the partition is 177.5 N.

Using Newton's law of motion we have,

$a\ =\ \frac{Force}{m_A\ +\ m_B}$

or $a\ =\ \frac{177.5}{5+10}\ =\ 11.83\ m/s^2$

For block A :

$F_A\ =\ m_Aa$

or $=\ 5\times 11.83\ =\ 59.15\ N$

So the required normal force is = 192.15 - 59.15 = 133.35 N.

(a) Using Newton's second law of motion we can write :

$F\ =\ ma$

or $=\ 15\times0.5\ =\ 7.5\ N$ Its direction is in the direction of motion of trolley.

The frictional force is $f\ =\ \mu mg$

or $=\ 0.18\times 15\times 10\ =\ 27\ N$

Since the frictional force is greater than the applied force so the block will appear to be at rest when seen by any stationary person.

(b) With reference to the observer moving with trolley, the trolley will be at rest as a pseudo force will act to balance out the frictional force. In relative motion both are moving together, thus are rest with respect to each other.

Using Newton's second law of motion we can write :

$F\ =\ ma$

$=\ 40\times 2\ =\ 80\ N$

Also, the frictional force is given by :

$f\ =\ \mu mg$

or $=\ 0.15 \times 40 \times 10\ =\ 60\ N$

Thus net force acting is : 80 - 60 = 20 N.

The backward acceleration is :

$a_b\ =\ \frac{20}{40}\ =\ 0.5\ m/s^2$

Now using the equation of motion we can write :

$s\ =\ ut +\ \frac{1}{2}at^2$

or $5\ =\ 0\ +\ \frac{1}{2}(0.5)t^2$

Thus $t\ =\ \sqrt{20}\ s$

And the distance travelled by truck is :

$s\ =\ ut +\ \frac{1}{2}at^2$

or $=\ 0 +\ \frac{1}{2}\times 2 (\sqrt{20})^2$

or $=\ 20 \ m$

Frequency of revolution is :

$=\ \frac{100}{ 3\times60}\ =\ \frac{5}{9}\ rev/sec$

(i) Case 1 :- When coin is placed at 4 cm :

Angular frequency :

$\omega\ =\ 2 \pi v$

or $=\ 2 \pi \times \frac{5}{9}\ =\ 3.49\ s^{-1}$

The frictional force is given by :

$f\ =\ \mu mg$

or $=\ 0.15\times m\times 10\ =\ 1.5m\ N$

Thus the centripetal force will be :

$F_c \ =\ mr\omega^2$

or $=\ m\times 0.04 (0.39)^2\ =\ 0.49m\ N$

Since frictional force is greater than the centripetal force so coin will revolve around the record.

(ii) Case 2:- When the coin is placed at 14 cm :

The centripetal force will be :

$F_c \ =\ mr\omega^2$

or $=\ m\times 0.14 (0.39)^2\ =\ 1.7m\ N$

Since frictional force is lesser than the centripetal force so the coin will slip from the record.

The motorcyclist does not drop down when he is at the uppermost point because of their weight and the normal force is balanced by the centripetal force .

$F_N\ +\ F_g\ =\ ma_{centripetal }$

or $F_N\ +\ mg\ =\ \frac{mv^2}{r}$

At minimum velocity, the normal reaction is zero.

So the equation becomes :

$mg\ =\ \frac{mv_{min}^2}{r}$

or $v_{min}\ =\ \sqrt{rg}$

or $=\ \sqrt{25\times 10}\ =\ 15.8\ m/s$

Frequency of rotation is :

$=\ \frac{200}{60}\ =\ \frac{10}{3}\ rev/sec$

The required condition so that man will not fall :

$mg\ <\ f$

or $mg\ <\ \mu F_N$

or $mg\ <\ \mu mr\omega^2$

or $\omega\ > \sqrt{\frac{g}{\mu r}}$

And thus :

$\omega\ _{min}\ =\ \sqrt{\frac{10}{0.5\times 3}}\ =\ 4.71\ rad\ s^{-1}$

Thus the required minimum rotational speed is 4.71 rad/s.

The FBD of the loop is given below :

Using equilibrium conditions we can write :

$mg\ =\ N\cos \Theta$

and $ml \omega ^2\ =\ N\sin \Theta$

Consider $\Delta$ OPQ, we have :

$\sin \Theta\ =\ \frac{l}{R}$

or $l\ =\ R\ \sin \Theta$

Using l in above equation we get :

$m(R \sin \Theta) \omega ^2\ =\ N\sin \Theta$

or $mR \omega ^2\ =\ N$

And $mg\ =\ (mR \omega^2)\cos \Theta$

Thus $\cos \Theta \ =\ \frac{g}{R \omega ^2}$

Since $\omega\ =\ \sqrt{\frac{2g}{r}}$

Substituting the value of $\omega$ in the above equation:-

$\frac{2g}{R}\ =\ \frac{g}{R \cos \Theta}$

Thus $\cos \Theta \ =\ \frac{1}{2}$

or $\Theta \ =\ 60^{\circ}$

Chapter 5 physics class 11 of motion is an important chapter in Mechanics. Students can score good marks after studying laws of motion NCERT solutions. Yes, if a student has a clear understanding of all three laws of motion which is given in chapter 5 class 11 physics , they will be able to relate these laws to various day-to-day activities and phenomena.

Regular practice is essential for developing a good grasp of the class 11 physics laws of motion. By practising regularly, students can enhance their problem-solving skills and confidence in applying the laws of motion to everyday situations. To reinforce their learning and verify their answers, students can refer to NCERT Solutions for Class 11 Physics Chapter 5 Laws Of Motion or student can download solution of laws of motion class 11 pdf while practising.

Laws of Motion Class 11 NCERT Solutions: Important Formulas and Diagrams + eBook link

Here, you'll find the key formulas and diagrams from this chapter's NCERT solutions. These tools make syllabus review efficient, aid concept understanding, and simplify homework tasks—enhancing your learning journey.

• Linear momentum

JEE Main Highest Scoring Chapters & Topics
Just Study 40% Syllabus and Score upto 100%

[SI unit - kg-m/s and dimension[MLT-1]

• Newton's Law

1st law(Law of Inertia): An object at rest will remain at rest, and an object in motion will continue moving with a constant velocity unless acted upon by an external force. Mathematically, it can be expressed as

F = 0, or F = ma = 0

FAB=-FBA

• Frictional Force

Friction force(Ff) = μN

Static friction(Fs) = μsN

Kinetic friction (Fk) = μkN

Angle of Friction (tanΘ) =μsN/N=μs

Note: Angle of repose(Θ)= Angle of friction (μs)

• Kinematics of Circular Motion

 Angular Variables Linear Variables Angular displacementc= Θ Distance travelled = S Angular Velocity (ω) =dΘ/dt Speed (V) =ds/dt Angular acceleration (α) =dω/dt=d2Θt/dt2=ω (dω/dΘ) Tangential acceleration (a) =dv/dt=d2s/dt2=v (dv/ds) Centripetal acceleration(ac) =v2/r

Importance of NCERT Solutions for Class 11 Physics Chapter 5 Laws of Motion:

To understand the solutions of NCERT Class 11 Physics Chapter 5 Laws of Motion, it is necessary to know how to draw a free-body diagram. To familiarise with free body diagrams practise as many problems as possible. NCERT solutions for Class 11 are important for competitive exams like NEET and JEE Main and final exams of Class 11 also. NCERT Solutions for Class 11 Physics Chapter 5 Laws of Motion helps to do well in these exams.

Key Features of Laws of Motion Class 11 NCERT Solutions

• These class 11 physics ch 5 NCERT solutions provide a repository of essential formulas, enabling a clear understanding of the fundamental principles of motion.
• The inclusion of diagrams enhances visualization, aiding students in grasping intricate concepts related to motion.
• Each problem is solved methodically, guiding students through the application of laws of motion and fostering a systematic problem-solving approach.
• The class 11 physics chapter 5 exercise solutions elucidate underlying concepts, ensuring students not only solve problems but also comprehend the reasoning behind each step.
• The concise presentation of formulas and diagrams supports efficient revision, allowing students to recapitulate the laws of motion class 11 numericals with solutions swiftly.
• These NCERT solutions for class 11 physics chapter 5 pdf download cater to homework assignments, making it easier for students to complete tasks accurately and effectively.

NCERT Solutions for Class 11 Physics Chapter Wise

 Chapter 1 Physical world Chapter 2 Chapter 3 Motion in a straight line Chapter 4 Chapter 5 Laws of Motion Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15

NCERT Physics Exemplar Solutions Class 11 For All The Chapters:

 Chapter 1 Physical World Chapter 2 Units and Measurements Chapter 3 Motion in a Straight Line Chapter 4 Motion in a Plane Chapter 5 Laws of Motion Chapter 6 Work, Energy, and Power Chapter 7 System of Particles and Rotational Motion Chapter 8 Gravitation Chapter 9 Mechanical Properties of Solids Chapter 10 Mechanical Properties of Fluids Chapter 11 Thermal Properties of Matter Chapter 12 Thermodynamics Chapter 13 Kinetic Theory Chapter 14 Oscillations Chapter 15 Waves

Subject wise NCERT Exemplar solutions

Feel confident in your understanding of the class 11 physics ch 5 NCERT solutions - Laws of Motion. If any doubts arise while using these solutions or if you require further clarification on any questions, don't hesitate to leave a comment below. Your success is our priority. Best of luck, and excel in your exams!

1. How many questions can be expected for JEE Main from laws of motion

One question can be expected for JEE Main from the chapter laws of motion. The concepts studied in this NCERT chapter will be applied in the upcoming chapters of Class 11 NCERT book for Physics.

2. What is the weightage of laws of motion for the NEET exam

3 % questions can be expected for NEET, from the NCERT chapter Laws of Motion. For more questions practice using NCERT exemplar for Class 11 Physics.

3. What is law of motion physics class 11 chapter 5 ?

The laws of motion are a set of three fundamental principles formulated by Sir Isaac Newton in the 17th century. They are the cornerstone of classical mechanics and form the basis for understanding the motion of objects and the forces acting upon them.

In phy class 11 ch 5, the Laws of Motion are discussed in Chapter 5, which covers the following topics:

• The first law of motion: The law of inertia, which states that an object at rest will remain at rest, and an object in motion will continue in motion with a constant velocity unless acted upon by an external force.

• The second law of motion: The law of acceleration, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

• The third law of motion: The law of action and reaction, which states that for every action, there is an equal and opposite reaction.

4. What is the law of motion or nlm class 11 formulae?

physics class 11th chapter 5 laws of motion are set of three fundamental principles in physics that describe the behaviour of objects and the forces acting upon them.

The three laws of motion can be expressed mathematically in the following formulas:

• First Law of Motion (Law of Inertia):

F = 0 (If the net external force acting on an object is zero, then its velocity will remain constant.)

• Second Law of Motion (Law of Acceleration):

F = m x a (The net force (F) acting on an object is equal to its mass (m) multiplied by its acceleration (a).)

• Third Law of Motion (Law of Action and Reaction):

F₁ = -F₂ (For every action, there is an equal and opposite reaction force.)

5. What is Newton's first law called?

Newton's first law is called the Law of Inertia. It states that an object at rest will remain at rest, and an object in motion will continue in motion with a constant velocity in a straight line, unless acted upon by an external force.

6. How many question are present in class 11 physics chapter 5 ncert solutions?

A total of 40 questions are present in chapter 5. question number 5.1 to 5.23 (Exercise solution) and question number 5.24 to 5.40 (additional exercise).

7. Is class 11 physics chapter 5 ncert solution important?

Yes, Class 11 Physics Chapter 5 NCERT solutions on Laws of Motion are important as they provide essential understanding and problem-solving guidance for Newton's laws, forming a crucial foundation for further physics concepts and exams

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