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Have you ever wondered how sportsmen determine how fast they are racing or why cars reduce in speed when a driver presses a brake? Motion is the very essence of our day-to-day lives through a ride on the roller coaster or going down the street or traveling in a bus. Chapter 7 Motion of Class 9 Science studies the scientific laws that govern such everyday phenomena and in this manner, the students are able to relate what is learnt in the classroom with the observations in life. These NCERT solutions are thoroughly delivered by subject experts and in a simple-to-understand pattern in a way that the students will study more and with interest.
The chapter also gives enough chances to the students to exercise the important concepts, that include speed, velocity, acceleration, displacement and distance by completing numerous solved examples, and problems with numbers. These NCERT solutions for class 9 Science aid in the mastering of the logic and application of concepts of motion. The NCERT Solutions have solved In-text Questions to get an in-depth perception of concepts in the textbook, problem solving skills are expanded with some solved exercise questions, Higher Order Thinking Skills (HOTS) questions for advanced knowledge and thinking, all Important topics such as types of motion, graphs of motion and equations of motion are covered and approach to solve questions which offers step-by-step plan to adequately address both the theory and the numericals.
The chapter Motion emphasizes essential concepts such as speed, velocity, acceleration, and types of motion, supported by a variety of questions and answers aimed at strengthening these fundamentals. These solutions are especially useful for self-study, enabling students to clearly understand the core ideas and improve their performance in exams.
Answer:
Yes, an object has moved through a distance can have zero displacements.
If an object moves and returns to the original position, the displacement will be zero. Consider the movement in a circular path. A man walks from point A in a circular path in a park and comes back to point A.
The distance traveled is equal to the circumference of the circular path, but displacement is zero.
Answer:
Side of the square field =
According to question,
He completes 1 round in
Now,
Number of round trips completed traveling =
We know, in 3 round trips the displacement will be zero.
In
Q 3. Which of the following is true for displacement?
(b) Its magnitude is greater than the distance traveled by the object.
Answer:
(a) The first statement is false. Because displacement can be zero when the initial point coincides with the final point.
(b) The second statement is false. The magnitude of displacement can never be greater than the distance travelled by the object. It can be either equal or less.
Q 1. Distinguish between speed and velocity.
Answer:
Speed | Velocity |
Speed is the distance travelled by an object in unit time |
Velocity is the speed of an object moving in a definite direction. |
Speed is a scalar quantity | Velocity is a vector quantity |
Speed does not depend on the direction | Velocity changes with change in direction |
Speed can never be negative | Velocity can be positive, negative or zero. |
Answer:
When the total distance traveled by the object is equal to the displacement, the magnitude of the average velocity will be equal to the average speed. Average speed is the total distance upon the time taken, whereas average velocity is the total displacement upon time taken.
Q 3. What does the odometer of an automobile measure?
Answer:
Odometer is a device that measures the total distance traveled by automobile.
Q 4. What does the path of an object look like when it is in uniform motion?
Answer:
An object is having a uniform motion if it covers equal distance in equal interval of time (which implies speed is constant!). So the path can be straight or curved.
For eg. Consider a circular path. For understanding purposes, divide the circumference of the circle in six equal parts each subtending
Answer:
Given, the signal travels at the speed of light,
Time taken by the signal =
Let the distance of the spaceship from the ground station be
We know,
Therefore, the distance of spaceship from the ground station is
Q 1. When will you say a body is in
Answer:
(i) If the velocity of an object traveling in a straight line increases or decreases by equal amounts in equal intervals of time, then the acceleration of the object is said to be uniform. For example, An apple having a free-fall motion.
(ii) On the other hand, if the velocity of the object increases or decreases by unequal amounts in equal intervals of time, then the acceleration of the object is said to be non-uniform. For example, A car travelling along a straight road increasing its speed by unequal amounts in equal intervals of time.
Q.2 A bus decreases its speed from 80 km h-1 to 60 km h-1 in 5 s. Find the acceleration of the bus.
Answer:
(We know,
Given, Initial speed of the bus,
The final speed of the bus,
Time is taken,
We know,
The negative sign implies retardation.
Therefore, the acceleration of the bus is
Or, the retardation(de-acceleration) of the bus is
Answer:
(We know,
Given, The train starts from rest. Hence, the initial speed of the train =
Final speed of the train =
Time taken,
We know,
Therefore, the acceleration of the train is
Q 1. What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?
Answer:
Distance-time graph is the plot of distance travelled by an object along x-axis against time along y-axis.
For the uniform motion of an object, the distance-time graph is a straight line with a constant slope.
For non-uniform motion of an object, the distance-time graph is a curved line with an increasing or decreasing slope.
Answer:
If the distance-time graph of an object is a straight line parallel to the time axis, it means that the distance of the object is the same from its initial position at any point of time. This implies that the object is not moving and is at rest.
Answer:
If the speed-time graph of an object is a straight line parallel to the time axis, it means that the speed of the object is not changing with time. Hence the speed of the object is constant. This also implies that the acceleration of the object is zero.
Q4. What is the quantity which is measured by the area occupied below the velocity-time graph?
Answer:
The area occupied below the velocity-time graph denotes the total distance travelled by an object in the given time frame.
We know,
Answer:
Given, The bus starts from rest. Hence, the initial speed of the bus =
Acceleration of the bus,
Time is taken,
(a) We know,
Therefore, the speed acquired by the bus is
Answer:
Given, The bus starts from rest. Hence, the initial speed of the bus, u =
Acceleration of the bus,
Time taken,
(b) We know,
Therefore, the distance travelled by bus is
Answer:
(We know,
Given, Initial speed of the train,
Acceleration of the train,
Since, the train has to be brought to rest, final speed of the train,
We know,
Therefore, the train travels a distance of
Answer:
Given, The trolley starts from rest. Hence, the initial speed of the trolley,
Acceleration of the trolley,
Time is taken,
We know,
Therefore, the velocity of the trolley after 3 sec is
Answer:
Given, Initial speed of the racing car, u =
Acceleration of the car,
Time taken,
We know,
Therefore, the distance travelled by the racing car in
Answer:
Taking upward direction as positive (+) direction:
Given,
The stone will move up until its velocity becomes zero.
We know,
Therefore, the stone reaches to a height of
Now,
We know,
Therefore, the time taken by the stone to reach the maximum height is
Answer:
Given, Diameter of the circular track =
The athlete completes one round of a circular track in 40 s.
In
Distance travelled by the athlete =
Also, number of rounds the athlete will complete in
Therefore, the final position of the athlete after
(3 complete rounds and one half round.)
Hence, displacement of the athlete = magnitude of diameter of the circle =200m
Answer:
Given,
(a) Distance between A and B =
Time taken to reach from A to B =
And, Average velocity from A to B =
(In this case, average speed is equal to the average velocity)
(b) Distance travelled from A to reach C =
And, Displacement from A to C =
Also, time taken to reach C from A =
And, Average velocity from A to C =
(In this case, average speed is not equal to the average velocity)
Q 3. Abdul, while driving to school, computes the average speed for his trip to be
Answer:
Given, Average speed while going to school,
And Average speed while returning back from school,
Let the distance between starting point and school be
And time taken by Abdul during the two trips be
We know,
And,
Now, Total distance that Abdul covers =
And total time Abdul takes to cover this distance =
Therefore, the average speed for Abdul's trip is
(Note:
Q 4. A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of
Answer:
Given, The motorboat starts from rest. Hence, initial speed of the motorboat, u =
Acceleration of the motorboat,
Time taken,
We know,
Therefore, the distance travelled by the motorboat is
Answer:
The initial speed
After 5 sec the car stops
The graph is represented by the blue line ( x-axis is time and the y-axis is speed)
For the car with 3Kmh -1 . Initial speed
The area covered by the blue graph is greater than the golden graph so the car with 15 m/s initial velocity travells large distance.
Which of the three is travelling the fastest?
Answer:
Given is a distance-time graph. The slope of this graph gives us speed. Hence, the graph with the highest slope will have the highest speed.
Since B has the highest slope(inclination), it travels the fastest.
Are all three ever at the same point on the road?
Answer:
Given is a distance-time graph. Any point on the curve will give the distance of object from O. Since there is no intersection point of all the three graphs, they never meet at the same point on the road.
(Although any two of them do meet at some point on the road!)
How far has C travelled when B passes A?
Answer :
Given is a distance-time graph. Any point on the curve will give the distance of object from O. To find how far C has travelled when B passes A, draw a perpendicular from the intersection point of A and B on time axis. The point where it intersects on the C graph, from C draw a perpandicular to y axis . Therefore, distance travelled by C will be (Final distance from O - Initial distance from O)
Therefore, C has traveled 6.5 km when B passes A.
How far has B travelled by the time it passes C?
Answer:
Given is a distance-time graph. The graph of B and C intersect at a point whose y-coordinate is 5. Hence, B has travelled
Answer:
Considering downward direction as positive direction.
Given, Height from which ball is dropped,
Acceleration of the ball,
Initial velocity,
(i) We know,
Therefore, the ball will strike the ground with a velocity of
(ii) Now, we know,
Therefore, the ball reaches the ground in
Note:
Q 8.(a) The speed-time graph for a car is shown is Figure:
Answer:
Given is a speed-time graph. The area under the curve will give the distance travelled by the car.
In time
Considering this part of the graph as a quarter of a circle whose radius = 4 unit.
Therefore, required area =
Therefore, distance the car travelled in the first 4 seconds is
Q 8. (b) The speed-time graph for a car is shown is Figure:
Which part of the graph represents uniform motion of the car?
Answer:
In uniform motion, the speed of car will become constant which is represented by line parallel to the time axis. In the given figure, the straight line graph from
Q 9. (a) State which of the following situations are possible and give an example for each of these: an object with a constant acceleration but with zero velocity
Answer:
(a) The given situation is possible.
When an object is thrown upwards (under gravity only), it reaches to a maximum height where its velocity becomes zero. However, it still has an acceleration acting in the downward direction (acceleration due to gravity).
Note: This is possible for a given point of time, however, it is not possible for a period of time.
Q 9.(b) State which of the following situations are possible and give an example for each of these: an object moving with an acceleration but with uniform speed.
Answer:
(b) The given situation is possible.
An object moving in a circular path with uniform speed, i.e covering equal distance in equal amount of time is still under acceleration. Because, the velocity keeps on changing due to continuous change in the direction of motion. Therefore, circular motion is an example of an object moving with an acceleration but with uniform speed.
Q 9. (c) State which of the following situations are possible and give an example for each of these: an object moving in a certain direction with an acceleration in the perpendicular direction.
Answer:
(c) The given situation is possible.
For an object moving in a circular path with constant speed, the direction of its velocity at any point will be tangential to that point. However, its acceleration will be directed radially inwards. (Constant speed but still having an acceleration - Due to continuous change in direction.)
Answer:
Given, Radius of the circular orbit =
The satellite takes 24 hours to revolve around the earth.
We know,
Therefore, the speed of the artificial satellite is
Q1:
The velocity-time graph of an object is shown in the figure. Identify the correct statement(s) regarding this graph.
(i)This is a non-uniform velocity-time graph of the object.
(ii) The velocity of the object is increasing at the same rate during OP and QR.
(iii) The velocity of the object is decreasing at the same rate during PQ and RT.
Answer:
From the graph, the velocity of the object is increasing at a constant rate for OP and QR and decreasing at a constant rate for PQ and RT. However, the rate of increasing or decreasing the velocity is not the same for all intervals. It is a non-uniform velocity-time graph.
Hence, the answer is the option (1).
Q2:
A train is moving at a speed of 40 km/hr at 10:00 a.m., and at 50 km/hr at 10:02 a.m.. Assuming that the train moves along a straight track and the acceleration is constant, find the value of the acceleration.
Answer:
Q3:
While driving through Napa you observe a hot air balloon in the sky with tourists on board. One of the passengers accidentally drops a wine bottle and you note that it takes 2.3 seconds for it to reach the ground. Find how high is the balloon.
Answer:
given wine bottle is dropped, i.e.,u=0
Q4:
A person starts jogging on a circular track and completes 5 full rounds. The circumference of the circular track is 88 m. Then find the net velocity of that person.
Answer:
Since the net displacement is zero, then the net velocity will be zero.
Q5:
A bus covers a distance of 250 km from Delli to Jaipur towards West in 5 hours in the morning and returns to Dellii in the evening covering the same distance of 250 km in the same time of 5 hours. Find (a) the average speed, and ( b ) the average velocity, of the bus for the whole journey.
Answer:
(a)
(b) In this case, the bus travels 250 km from Della to Jaipur towards the West and then comes back to the starting point Dellhi in the reverse direction. So, the total displacement (or total distance travelled in a specified direction) will be 250 km-250 km=0
NCERT Solutions for Class 9 Science Chapter 7 – Motion cover all the key topics that explain how objects move, including concepts like speed, velocity, acceleration, and graphical representation of motion. These topics help students understand the fundamental laws that govern motion in everyday life.
7.1 Describing Motion
7.1.1 Motion along a straight line
7.1.2 Uniform Motion and Nonuniform Motion
7.2 Measuring the rate of motion
7.2.1 Speed with Direction
7.3 Rate of Change of Velocity
7.4 Graphical Representation of Motion
7.4.1 Distance- Time Graphs
7.4.2 Velocity-Time Graphs
7.5 Equations of Motion by Graphical Method
7.5.1 Equation for Velocity-Time Relation
7.5.3 Equation for Position-Velocity Relation
7.6 Uniform Circular Motion
Speed
Velocity
Where:
Unit:
1.
2.
3.
Where:
Average Speed
Read the question in order to know the quantities provided (such as distance, time, or the type of motion).
Determine the nature of the motion involved; is it non-uniform or uniform (with a steady speed).
Understand what is asked, i.e. which speed, in which direction, which distance is covered or which comparison of two motions.
Apply conceptual knowledge: apply purpose of the question to definitions of motion such as distinction between speed and velocity.
It is also important to draw diagrams or motion graphs (as appropriate) to make the problem easier to understand.
Write down and organize the information in a step-by-step kind of representation before one tries the solution.
Break down units and directions Units and directions are important to analyze especially when it comes to displacement and velocity.
Distance is the total path covered (scalar), while displacement is the shortest path from start to end (vector).
Distance is the total path covered (scalar), while displacement is the shortest path from start to end (vector).
When an object covers equal distances in equal time intervals.
It gives the speed of the object.
To understand how things move and to solve real-life problems like travel, transport, etc.
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