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Edited By Safeer PP | Updated on Aug 08, 2022 05:20 PM IST

NCERT Exemplar Class 11 Physics solutions chapter 4 takes the concept of motion a step forward, by describing an object's motion in a two or three-dimensional plane. NCERT Exemplar Class 11 Physics chapter 4 solutions use the operations and graphical representation of vectors to help understand the motion in a plane. This chapter of NCERT Class 11 Physics Solutions revolves around a constantly accelerated motion in a plane and the relative velocity in two dimensions. Students would explore the concepts surrounding projectile motion and circular motion.

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This Story also Contains

- NCERT Exemplar Class 11 Physics Solutions Chapter 4 Motion in a Plane
- NCERT Exemplar Class 11 Physics Solutions Chapter 4 MCQI
- NCERT Exemplar Class 11 Physics Solutions Chapter 4 MCQII
- NCERT Exemplar Class 11 Physics Solutions Chapter 4 Very Short Answer
- NCERT Exemplar Class 11 Physics Solutions Chapter 4 Short Answer
- NCERT Exemplar Class 11 Physics Solutions Chapter 4 Long Answer
- Main Subtopics in NCERT Exemplar Class 11 Physics Solutions Chapter 4 Motion in a Plane
- What Will The Students Learn in NCERT Exemplar Class 11 Physics Solutions Chapter 4?
- NCERT Exemplar Class 11 Physics Solutions Chapter-Wise
- Important Topics To Cover For Exams in NCERT Exemplar Solutions for Class 11 Physics Chapter 4
- NCERT Exemplar Class 11 Solutions

For a smooth learning curve and better understanding, students can avail the NCERT Exemplar Class 11 Physics solutions chapter 4 PDF Download function. These solutions are made by experts holding eminence in their respective fields. These solutions would help explain the concepts of 2D/3D motion well to score well in the final exams.

Question:4.1

The angle between and is

(a)

(b)

(c)

(d)

Answer:

The answer is the option (b),We know from the formula that

Given that and

Hence the angle is

Question:4.2

Which one of the following statements is true?

(a) A scalar quantity is the one that is conserved in a process.

(b) A scalar quantity is the one that can never take negative values.

(c) A scalar quantity is the one that does not vary from one point to another in space.

(d) A scalar quantity has the same value for observers with different orientations of the axes.

Answer:

The answer is the option (d), A scalar quantity has the same value for observers with different orientations of the axes.Unlike vector quantities, a scalar quantity has no dependence on the direction, and hence its value remains the same for all the orientations of the axes.

Question:4.3

Figure 4.1 shows the orientation of two vectors u and v in the XY plane.

If and

which of the following is correct?

(a) a and p are positive while b and q are negative.

(b) a, p and b are positive while q is negative.

(c) a, q and b are positive while p is negative.

(d) a, b, p and q are all positive.

Answer:

The answer is the option (b) a, p and b are positive while q is negative.Explanation:

Now, and

For vector u, both the components a and b are in the positive direction of the x-axis. Hence, they are positive.

For vector v, p is in the positive direction, but q is in the opposite direction. Hence, p is positive, and q is negative.

Question:4.4

The component of a vector r along X-axis will have maximum value if

(a) r is along positive Y-axis

(b) r is along positive X-axis

(c) r makes an angle of 45° with the X-axis

(d) r is along negative Y-axis

Answer:

The answer is the option (b) r is along positive X-axisThe maximum value of , which is when .

Hence, for the vector r, the maximum value will be when it is along the positive x-axis.

Question:4.5

The horizontal range of a projectile fired at an angle of is 50 m. If it is fired with the same speed at an angle of , its range will be

a) 60 m

b) 71 m

c) 100 m

d) 141 m

Answer:

The answer is the option (c) 100 mAccording to the formula:

Given in the question:

Putting in the formula we get:

For

The value of the range is:

Question:4.6

Consider the quantities pressure, power, energy, impulse gravitational potential, electric charge, temperature, area. Out of these, the only vector quantities are

a) impulse, pressure, and area

b) impulse and area

c) area and gravitational potential

d) impulse and pressure

Answer:

The answer is the option (b) impulse and areaImpulse is a vector quantity and not a scalar quantity as the impulse is the rate of change of momentum, and it involves direction.

The area is a vector quantity

Question:4.7

In a two dimensional motion, instantaneous speed v0 is a positive constant. Then which of the following are necessarily true?

a) the average velocity is not zero at any time

b) average acceleration must always vanish

c) displacements in equal time intervals are equal

d) equal path lengths are traversed in equal intervals

Answer:

The answer is the option (d) equal path lengths are traversed in equal intervals.Question:4.8

In a two dimensional motion, instantaneous speed is a positive constant. Then which of the following are necessarily true?

a) the acceleration of the particle is zero

b) the acceleration of the particle is bounded

c) the acceleration of the particle is necessarily in the plane of motion

d) the particle must be undergoing a uniform circular motion

Answer:

The answer is the option (c) the acceleration of the particle is necessarily in the plane of motionQuestion:4.9

Three vectors A,B and C add up to zero. Find which is false.

(a) (A * B) * C is not zero unless B,C are parallel

(b) (A * B).C is not zero unless B,C are parallel

(c) If A,B,C define a plane, (A * B) *C is in that plane

(d)

Answer:

The answer is the option (a) and (c)Explanation:

Given

Option a :

(this cannot be zero)

Only if B and C are antiparallel or parallel will be zero

Hence for the whole quantity to be zero, should be true.

Option C :

X is perpendicular to the planes which have vector A and vector B

Vector Y is perpendicular to the planes which have vector A and vector B

Vector Y is perpendicular to the plane containing X and C which is, in turn, the plane containing vectors A, B and C

Question:4.10

It is found that This necessarily implies,

(a)

(b) A,B are antiparallel

(c) A,B are perpendicular

(d)

Answer:

The answer is the option (a)Explanation :

Squaring both sides and opening the brackets we get,

Question:4.11

Two particles are projected in air with speed , at angles and to the horizontal, respectively. If the height reached by the first particle is greater than that of the second, then tick the right choices

a) angle of project:

b) time of flight:

c) horizontal range:

d) total energy:

Answer:

The answer is the option (a) and (b)Explanation:

According to formula. Max height of a projectile is

Option a :

So,

So, and lies etween 0 and 90 degree i.e. acute

Option b :

Since

Question:4.12

A particle slides down a frictionless parabolic track starting from rest at point A (Fig. 4.2). Point B is at the vertex of parabola and point C is at a height less than that of point A. After C, the particle moves freely in air as a projectile. If the particle reaches highest point at P, then

(a) KE at P = KE at B

(b) height at P = height at A

(c) total energy at P = total energy at A

(d) time of travel from A to B = time of travel from B to P.

Answer:

The answer is the option (c)As we know through the energy conservation law, total energy at point P will be same as total energy at point A.

Hence, option c is correct.

Question:4.13

Answer:

The answer is the option (a) and (c)Option a:

The given relation is correct when the acceleration is uniform

Option c:

This is the relationship given in the question, but it is not possible as the LHS and RHS dimensions and do not match and hence the relationship cannot be considered valid.

Question:4.14

For a particle performing uniform circular motion, choose the correct statement(s) from the following:

(a) Magnitude of particle velocity (speed) remains constant.

(b) Particle velocity remains directed perpendicular to radius vector.

(c) Direction of acceleration keeps changing as particle moves.

(d) Angular momentum is constant in magnitude but direction keeps changing.

Answer:

The answer is the option (a), (b), and (c)Option a: speed is constant at all times in the case of uniform circular motion

Option b: in case of velocity, in a circular motion it is measured tangentially to the direction of motion of the particle which is in turn perpendicular to the radius.

Option c: the direction of the acceleration is in the direction of force always. This can concur with the newton’s second law of motion. So as the particle moves in the circular motion, the direction of force keeps on changing and hence that of acceleration also changes.

Question:4.15

For two vectors A and B, is always true when

(a)

(b)

(c) and A and B are parallel or anti parallel

(d) when either or is zero.

Answer:

The answer is the option (b) and (d)Explanation:

Given :

Now we square both sides and open the brackets to get:

So, we have, degree and

Hence option b and option d are correct.

Question:4.17

Answer:

A particle travelling in a projectile motion will definitely have a path which is parabolic in nature. The velocity of such a particle is always measured tangential to the path of motion. Point B is where the particle reaches maximum height during the projectile motion.Here we have the vertical and horizontal components of B which are and

Question:4.18

A ball is thrown from a roof top at an angle of above the horizontal. It hits the ground a few seconds later. At what point during its motion, does the ball have

a) greatest speed

b) smallest speed

c) greatest acceleration?

Answer:

The ball is thrown from point O. The angle with the horizontal is 45 degree. As the height increases from O to A, the speed decreases. At B, the speed becomes equal to its initial speed. The height decreases further from B to C and becomes maximum at point C.

a) greatest speed of the ball is at c as and

b) slowest speed will be at point A. here , and the horizontal speed is

c) the greatest acceleration will be the one caused by the gravitational force downward, which will be equal to g.

Question:4.19

A football is kicked into the air vertically upwards. What is its

a) acceleration

b) velocity at the highest point

Answer:

a) when the football is kicked into the air, the only force working on it is the gravitational force. Hence the acceleration will be caused due to this force which will be in the downward direction towards the centre of the Earth.b) when the ball is thrown upward, no horizontal forces act on it and hence the horizontal component velocity becomes nil. The vertical component of velocity at the highest point is . Hence, the net velocity when the ball reaches the highest point is also zero.

Question:4.20

A, B, and C are three non-collinear, non co-planar vectors. What can you say about direction of ?

Answer:

Given: A, B, and C are non-collinear and no co-planar vectors.For finding out the direction, we used the right-hand grip rule.

For , the direction will be in a plane perpendicular to the plane containing and .

However, for the direction of it will be perpendicular to both and the plane which has

Question:4.21

Answer:

Let v be the vertical velocity, and u be the horizontal velocity of the car.In the case of the ball, as it has both horizontal and vertical components of velocity, it will have a parabolic path when a person standing on a footpath sees the trajectory.

When a boy sitting in the same car sees the ball, the path will vertical up and down. However, he will be able to catch up with the ball provided the car moves at a constant velocity.

Question:4.22

Answer:

Given :now, in the direction of the ball, the speed of the car is

since the horizontal speeds are the same, in the situation of a ball thrown by the boy as soon as the car passes him, they also cover equal horizontal distances.

Now, when vertical components are considered, and the motion of the ball is vertically up-down as seen by the boy.

Question:4.23

Answer:

When we are dealing with projectile motion generally we neglect the air resistance. But if air resistance is included the horizontal component of velocity will not be constant and obviously trajectory will change.

Due to air resistance, particle energy, as well as horizontal component of velocity, keep on decreasing making the fall steeper than rise as shown in the figure.

When we are neglecting air resistance path was symmetric parabola (OAC). When air resistance is considered path is asymmetric parabola (OAB).

Question:4.23

Answer:

The horizontal and vertical components of the velocity decrease due to air resistance. So, as a result, the max height also becomes lesser than in the ideal case.

Now, and max height

So,

But, in the second case when , due to smaller time taken to rise, the overall time of flight for both cases stands equal

Question:4.24

Answer:

we assume that the bomb is dropped by the pilot t seconds vertically above Q before the target T

vertical component velocity of the bomb will be zero and the horizontal component value will be equal to that of the plane. So, the bomb covers distance TQ as a free fall.

Now,

So,

So, we get,

ut is the distance covered by plane or the bomb equal to PQ

hence,

now,

Question:4.25

Answer:

The angular acceleration will have its direction towards the centre and the value will beNow,

and

Acceleration of the person on the surface of the earth,

Now, At equator latitude = 0

Hence which is much smaller than the previous case.

b) acceleration of Earth revolving around the sun

and

Now,

Also,

Question:4.27

If and , then match the relations in column I with the angle between A and B in column II.** Column I Column II**

(a) (i)

(b) (ii)

(c) (iii)

(d) (iv)

Answer:

a) Matches with (ii)b) Matches with (i)

c) Matches with (iv)

d) Matches with (iii)

Question:4.28

If and then match the relations in column I with the angle between A and B in column II.** Column I Column II**

(a) (i)

(b) (ii)

(c) (iii)

(d) (iv)

Answer:

Given : anda) Matches with (iv)

b) matches with (iii)

c) matches with (i)

d) matches with (ii)

Question:4.29

Answer:

Packet speed = 125 m/s, height of hill = 500m

In order to cross the hill, the vertical component of the packet should be reduced to make the height of 500m attainable. The distance between canon and hill should also be half of that of the packet’s range.

Now,

now we consider the packet's vertical motion,

t= total time of flight = 10 sec

so,

so the distance between canon and hill is 750m

distance for which the canon needs to move

time taken for the canon to move

so the total time taken by the packet

Question:4.3

A gun can fire shells with maximum speed and the maximum horizontal range that can be achieved is

If a target farther away by beyond R has to be hit with the same gun as shown in the figure. Show that it could be achieved by rating the gun to a height at least

Answer:

The solution to this problem can be given in two ways:

i) the target is present at the horizontal distance of and is h meters below the projection point.

ii) the motion of projectile starting from point P till reaching point T. vertical height covered is -h and horizontal range is

max range of a projectile is given by

here,

we assume that the gun is raised to a height h to hit the target T

total range

the horizontal component of velocity is,

horizontal velocity at

vertical velocity at

now,

So,

Substituting the value of t in (1) we get,

hence proved.

Question:4.31

Answer:

a) expression of range on the plane surface

Now, and

at O and P,

So

where t = T

b) motion of particle along Y axis

So,

a) Now we continue the part a

c) on the axis X, L will be maximum when will be maximum

let

In order to make Z maximum, we put

Opening the brackets, we get

radian

Question:4.32

Answer:

The particle rebounds from P. when it strikes plane inclined at v0 speed. Hence the speed of particle after it rebounds from P will be v0 We assume the new axis X’OX and YOY’ axis at P as origin ‘O’. The components of g and v0 in the new OX and OY axis are:Focusing on the motion of the particle from O to A,

Here, t=T which is the time of flight

So, either

Question:4.34

A river is flowing due east with a speed 3m/s. A swimmer can swim in still water at a speed of 4 m/s (Fig. 4.8).

(a) If swimmer starts swimming due north, what will be his resultant velocity (magnitude and direction)?

(b) If he wants to start from point A on south bank and reach opposite point B on north bank,

(a) which direction should he swim?

(b) what will be his resultant speed?

(c) From two different cases as mentioned in (a) and (b) above, in which case will he reach opposite bank in shorter time?

Answer:

a) If swimmer starts swimming due north, what will be his resultant velocitydue north

due east

Now since both the directions are perpendicular,

in the North direction

b) The swimmer wants to start from point A on the south bank and reaches the opposite point B on the north bank

The swimmer makes an angle with the north.

From the figure we have the relation,

Henece

Now we calculate the value of θ through the below formula,

So, in th edirection from North to West

c) we need to find from the above two scenarios that for the swimmer to reach the opposite bank in the shorter time

we know that the velocity component perpendicular to the river is 4m/s

let us assume the width of the river to be ‘w’

Time taken - North

time taken in part b) when

taking ratio,

Now as,

So, the swimmer will take a shorter time in case a)

Question:4.35

A cricket fielder can throw the cricket ball with a speed vo. If he throws the ball while running with speed u at an angle to the horizontal, find

a) the effective angle to the horizontal at which the ball is projected in air as seen by a spectator

b) what will be time of flight?

c) what is the distance from the point of projection at which the ball will land?

d) find at which he should throw the ball that would maximise the horizontal range as found c)

e) how does for maximum range change if and

f) how does in e) compare with that for u = 0?

Answer:

a) u is the horizontal velocity with which the cricketer runs. The ball is thrown by him while running and hence the speed of ball also contains a component of the cricketer’s speed.Vertical component,

b) Time of flight

Since the ball returns back to the same position, Sy = 0

So,

Since T cannot be zero, we have

c) Maximum range

for the max range, the condition is

e) In the case when

(as is taken as an acute angle here)

hence,

for the case of u << v

Since is an acute angle here,

as u << v here, we can neglect the last term

For u >> v,

f) when

Question:4.36

Motion in two dimensions, in a plane can be studied by expressing position, velocity and acceleration as vectors in Cartesian co-ordinates where and are unit vector long x and y directions, respectively and and are corresponding components of A (fig.4.9). Motion can also be studied by expressing vectors in circular polar co-ordinates as where and are unit vectors along direction in which 'r' and are increasing.

(a) Express and in terms of and

(b) Show that both and are unit vectors and are perpendicular to each other.

(c) Show that where and

(d) For particle moving along a spiral given by where (unit), find dimensions of 'a'.

(e) Find velocity and acceleration in polar vector represention for particle moving along spiral described in (d) above.

Answer:

a)When we multiply 1 by and 2 by , we get :

When we multiply 1 by and 2 by we get :

Subtracting equation 5 from 4 and comparing the coefficients we get,

b) from equation 1 and 2, through the dot product method we get,

Since LHS elements cannot be zero,

and

c)

Since,

d)

now looking at the dimensions of the quantities on the LHS and the RHS,

e)

**Also, check NCERT Solution subject wise -**

- NCERT solutions for Class 11
- NCERT Solutions for Class 11 Maths
- NCERT Solutions for Class 11 Chemistry
- NCERT Solutions for Class 11 Biology

**Also, Read NCERT Notes subject wise -**

- NCERT Notes for Class 11 Maths
- NCERT Notes for Class 11 Physics
- NCERT Notes for Class 11 Chemistry
- NCERT Notes for Class 11 Biology

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Download EBook**Class 11 Physics NCERT Exemplar Solutions Chapter 4 Includes The Following Topics:**

- 4.1 Introduction
- 4.2 Scalars and vectors
- 4.3 Multiplication of vectors by real numbers
- 4.4 Addition and subtraction of vectors — graphical method
- 4.5 Resolution of vectors
- 4.6 Vector addition — analytical method
- 4.7 Motion in a plane
- 4.8 Motion in a plane with constant acceleration
- 4.9 Relative velocity in two dimensions
- 4.10 Projectile motion
- 4.11 Uniform circular motion

- Students would be able to link the concepts of motion in the previous chapter to this chapter and broaden their learning scope.
- This chapter will also introduce students to the vector operations used to determine the motion of an object with specific dimensions.
- NCERT Exemplar Class 11 Physics chapter 4 solutions would provide a graphical and analytical representation of vectors for a better understanding of motion.
- It answers questions and queries related to relative velocity in dimensions and constant acceleration.
- NCERT exemplar Class 11 Physics solutions chapter 4 also offers the opportunity to learn about the broad topic of projectile motion to determine a ball's trajectory in a cricket match or the launching of a satellite and its path.

· NCERT Exemplar Class 11 Physics solutions chapter 4 highlights the previous chapter of motion in a straight line to explain many of motion's concepts and terms in a plane. It talks about the different arithmetic expressions, including graphical and theoretical methods to add, subtract, multiply, and resolve vectors.

· This chapter covers dimensions' characteristics and how they're used to explain objects' straightforward motion in a 2D or 3D plane, be it in a constantly accelerated motion or a uniform circular motion.

· NCERT Exemplar Class 11 Physics solutions chapter 4 also talks about the broad applications of projectile motion in determining the future position or the direction of an object in motion and the significance of uniform circular motion. NCERT Exemplar Class 11 Physics chapter 3 solutions provides a comprehensive learning perspective that extends the relative velocity concepts.

Chapter 1 | Physical world |

Chapter 2 | Units and Measurement |

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 |

1. How to download these Solutions to Class 11 Chapter 4?

These Class 11 physics NCERT exemplar solutions chapter 4 can be downloaded in the browser by using the ‘download page’ option.

2. How can these solutions help in final exams?

NCERT Exemplar Class 11 Physics Solutions Chapter 4 can help you use the applications of motions in real life, understand and determine the position of objects in projectile motion, and help give an excellent academic performance in your final exams.

3. What are the essential topics of this chapter?

This chapter's essential topics are the Scalars and vectors, operations on vectors, motion in a plane, relative velocity, projectile, and uniform circular motion.

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