NCERT Solutions For Class 9 Science Motion

IN-TEXT QUESTIONS SOLVED

NCERT Textbook Page- 100
Question.1. An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.
Answer. Yes, the object inspite of moving through a distance can have zero displacement. Example, if an object travels from point ‘A’ and reaches to the same point ‘A’, then its displacement is ‘O’.

Question.2. A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds from his initial position?
Answer. Total distance = 40 m Time taken = 40 s
Total time taken by the farmer = 2 min 20 seconds =140 seconds … 140 -s- 40 = 3.5
The farmer completes 3 and a half round of the square. i.e., if he starts from A he reaches point ‘C ° after 2 minutes 20 seconds.
Displacement is AC.
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Question.3. Which of the following is true for displacement?
(a) It cannot be zero.
(b) Its magnitude is greater than the distance travelled by the object.
Answer. (a) False (b) False

NCERT Textbook Page- 102
Question.1. Distinguish between speed and velocity.
Answer.
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Question.2. Under what condition(s) is the magnitude of average velocity of an object equal to its average speed? –
Answer. The magnitude of average velocity of an object is equal to its average speed if the object moves in a straight line in a particular direction.

Question.3. What does the odometer of an automobile measure?
Answer. The odometer of an automobile measure the distance travelled by a vehicle.

Question.4.What does the path of an object look like when it is in uniform motion?
Answer. It is a straight line.

Question.5. During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is 3 x if ms’1.
Answer. Time taken = 5 minutes = 5 x 60 sec = 300 sec
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NCERT Textbook Page- 103
Question.1. When will you say a body is in
(i) uniform acceleration? (ii) non-uniform acceleration?
Answer. (i) Uniform acceleration: If the velocity of a body changes by equal amounts in equal interval of time, howsoever small or large these intervals may be, the acceleration is said to be uniform. Acceleration due to gravity is an example of uniform acceleration.
(ii) Non-uniform acceleration: If velocity changes by unequal amount in equal interval of time or if the direction of motion changes then the acceleration is said to be non-uniform. Acceleration of a train running from one station to another is a non-uniform acceleration.

Question.2. A bus decreases its speed from 80 km h’1 to 60 km hT1 in 5 s. Find the acceleration of the bus.
Answer.
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NCERT Textbook Page- 107
Question.1.What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?
Answer.
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Question.2. What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
Answer. The body is at rest.
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Question.3. What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time cuds?
Answer.
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The body is moving with a uniform speed and zero acceleration.

Question.4. What is the quantity which is measured by the area occupied below the velocity ¬time graph?
Answer. Distance travelled.

NCERT Textbook Page- 109-110
Question.1. A bus starting from rest moves with a uniform acceleration of 0.1 ms -2 for 2 minutes. Find (a) the speed acquired, (b) the distance travelled.
Answer.
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Question.2. A train is travelling at a speed of 90 km h -1. Brakes are applied so as to produce a uniform acceleration of-0.5 ms-2. Find how far the train will go before it is brought to rest.
Answer.
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Question.3. A trolley, while going down an inclined plane, has an acceleration of 2 cm s-2. What will be its velocity 3 s after the start?
Answer.
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Question.4.A racing car has a uniform acceleration of 4 ms~2. What distance will it cover in 10 s after start?
Answer.
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Question.5.A stone is thrown in a vertically upward direction with a velocity of 5 ms~1. If the acceleration of the stone during its motion is 10 ms~2 in the downward direction, what will be the height attained by the stone and how much time will it take to reach there?
Answer.
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The height attained by the stone is 1.25 m and time required to reach there is 0.5 s.

QUESTIONS FROM NCERT TEXTBOOK

Question.1.An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s?
Answer.
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Question.2.Joseph jogs from one end A to the other end B of a straight 300 m road in 2 minutes 30 seconds and then turns around and jogs 100 m back to point C in another 1 minute. What are Joseph’s average speeds and velocities in jogging (a) from A to B and (b) from A to C?
(a) From A to B Time for A -> B
Answer.
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Question.3.Abdul, while driving to school, computes the average speed for his trip to be 20 km hr-1. On his return trip along the same route, there is less traffic and the average speed is 30 km K1. What is the average speed for Abdul’s trip?
Answer.
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Question.4. A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of 3.0 ms-2 for 8.0 s. How far does the boat travel during this time?
Answer.
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Question.5. A driver of a car travelling at 52 km h 1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Answer.
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Question.6. Figure given below shows the distance-time graph of three objects A. B and C, study the graph and answer the following questions.
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(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
Answer. (a) B is travelling fastest.
(b) No, three lines do not meet at any point.
(c) When B passes A, C is at a distance approximately 8 km from origin.
(d) By the time B passes C, it has travelled 5.5 km.

Question.7. A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 ms 2, with what velocity will it strike the ground?
Answer.
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Question.8. The speed-time graph for a car is shown in the figure given below.
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(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which pari of the graph represents uniform motion of the car?
Answer. (a) The distance travelled by car in the first 4 seconds is approximately 12 m.
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(b) The uniform motion of the car is shown after 5.5 s.

Question.9. State which of the following situations are possible and give an example for each of these: (a) an object with a constant acceleration but with zero velocity
(b) an object moving in a ceriain direction with an acceleration in the perpendicular direction.
Answer. (a) Free fall due to gravity
(b) Object moving in a circular path

Question.10. An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth.
Answer.
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MORE QUESTIONS SOLVED

I. Multiple Choice Questions
Choose the correct option:
1. A car travels a distance of 100 km in 2 hours.
(a) Its average speed is 50 km/h.
(b) The car did not travel at 50 km/h all the time.
(c) The car travelled 50 km/h all the time.
(d) all of the above
2. If an object’s speed and direction of motion changes. Then it is moving with
(a) uniform speed
(b) uniform velocity
(c) non-uniform velocity
(d) both (b) and (c)
3. The distance-time graph of an object is shown in the figure given below. The object is
ncert-solutions-class-9-science-motion-2-26
(a) at rest
(b) is making with constant speed Time
(c) is making with constant velocity
(d) is making with constant acceleration
4. The area under the distance-time graph gives
(a) uniform speed
(b) non-uniform speed
(c) velocity and speed
(d) both (a) and (b)
5. The odometer of a car measures
(a) speed (b) velocity
(c) acceleration (d) distance
6.The unit m/s2 is of
(a) velocity (b) speed
(c) acceleration (d) deceleration
7.The velocity-time graph represents
ncert-solutions-class-9-science-motion-2-27
(a) body is in uniform motion
(b) body is stationary
(c) distance travelled by the body
(d) none of these
8. The area under velocity-time graph gives a physical quantity whose unit is
(a) m/s (b) m/s2
(c) m (d) m2
9. If a particle moves with a constant speed, the distance-time graph is
(a) straight line (b) curved line
(c) horizontal line to time (d) parallel line to velocity
10. An object moving with uniform circular motion shows (a) constant acceleration (b) constant velocity
(c) constant change in direction (d) constant change in motion
Answer. 1—(a). 2—(c), 3—(a), 4—(d), 5—(d), 6—(c), 7—(a), 8—(a), 9—-(a), 10—(c).

II. Very Short Answer Type questions

Question.1. Define uniform motion.
Answer. When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.

Question.2. Define speed.
Answer. It is defined as the distance travelled by an object in unit time. Its unit is m/s.

Question.3. Define average speed.
Answer. The total distance travelled by an object divided by the total time taken.

Question.4. Define velocity.
Answer. Velocity is the speed of an object moving in definite direction.

Question.5.Define acceleration.
Answer.Change in the velocity of an object per unit time.
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Question.6.While plotting a distance-time graph, why do we plot time on X-axis.
Answer.While plotting a distance-time graph, we should plot time on X-axis as, all independent quantities are plotted on X-axis.

Question.7.What is odometer?
Answer.Odometer is a device fitted in the automobiles to show the distance travelled.

Question.8.Draw a distance-time graph that represents uniform speed.
Answer.
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Question.9.With the help of distance-time graph show that the object is stationary.
Answer.
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Question.10.What does the area under velocity-time graph represent?
Answer.The area under the velocity-time graph represents the displacement.

Question.11.A body travels a distance from,A to B its physical quantity is measured to be -15 m/s. Is it speed or velocity? Give reason for the answer.
Answer.The physical quantity is – 15 m/s. It represents velocity because sign of speed cannot be a negative. Negative sign indicates the opposite direction.

Question.12.What type of velocity-time graph will you get for a particle moving with a constant acceleration?
Answer.For a particle moving with a constant acceleration velocity-time graph will be a straight line inclined to x-axis.

Question.13.Define uniform circular motion.
Answer.When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.

Question.14.What is deceleration?
Answer.When the speed of an object decreases, the object is said to be decelerating. In this case the direction of acceleration is opposite to the velocity of the object.

III. Short answer type questions

Question.1. Give the difference between distance and displacement.
Answer.
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Question.2. Give the difference between speed and velocity.
Answer.
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Question.3. Give the difference between acceleration and deceleration
Answer.
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Question.4. Differentiate between velocity and acceleration.
Answer.
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Question.5.help of graph, show the uniform acceleration and uniform retardation of a body.
Answer.
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OA – shows uniform acceleration.
OB – shows uniform retardation.

Question.6. What conclusion do you draw about acceleration of the particle in motion from given velocity-time graph?
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Answer.
(a) No acceleration
(b) Uniform acceleration

Question.7. A car accelerates uniformly from 20 km/h to 35 km/h in 5 s. Calculate (i) the acceleration and (ii) the distance covered by the car in that time.
Answer.
ncert-solutions-class-9-science-motion-2-37

Question.8.The odometer of a car reads 1800 km at the start of a trip and 2400 km at the end of the trip. If the trip took 10 h. Calculate the average speed of the car in km/h and m/s.
Answer.
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Question.9.An object travels 16 m in 4 s and then another 16 m in 3 s. What is the average speed of the object?
Answer.
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Question.10.It took 2 s after lightning for the sound of thunder to reach you. How far did the lightning struck?
Speed of sound is 346 m/s in air.
Answer.
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Question.11.Find the type of motion in the following case :
(a) A car travelling along a straight road, changes its speed.
(b) An athlete running a 100 m race.
(c) Moon revolving around the earth.
(d) An ant moving on the floor.
Answer.(a) Non-uniform motion (b) Uniform motion
(c) Uniform circular motion (d) Non-uniform motion

Question.12.What Conclusion that you draw about accelaration of the partical in motion from given velocity time graph?
Answer.
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Question.13.what the position for velocity time relation(v=u+at) by graphical method?
Answer.
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Question.14.. How can we get speed from distance-time graph?
Answer. Let us assume that an object moves with a uniform speed. The distance-time graph will be a straight line.
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Conclusion:
To find the speed from distance-time graph we can get its slope which is equal to the speed of the object.

Question.15.Represent a graph that shouts the following:
(a) Uniform speed (b) Non-uniform speed (c) Stationary object
Answer.Time is taken on X-axis as it is independent quantity and all dependent quantities are taken along Y-axis.
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Question.16.Draw graph to show the following:
(a) Uniform acceleration
(b) Non-uniform acceleration
(c) Uniform motion
Answer.
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Question.17.How can you get the distance travelled by on object from its speed-time graph?
Answer.
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To find the distance travelled by a body from its speed-time graph, we need to find the area enclosed by the graph.

IV. Long answer typed Questions

Question.1. (a) What is motion?
(b) State types of motion.
(c) Derive the unit for acceleration.
Answer. (a) Motion: An object is said to be in motion when its position changes with time. We describe the location of an object by specifying a reference point. Motion is relative.
The total path covered by an object is said to be the distance travelled by it.
(b) There are two types of motion: Uniform motion and non-uniform motion Uniform motion: When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.
Non-uniform motion: Motion where object cover unequal distances in equal intervals of time.
(c) Acceleration, ‘a’ is change in velocity per unit time.
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Question.2.(a) What is uniform circular motion?
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(b) An athlete runs on a circular track, whose radius is 50 m with a constant speed. It takes 50 seconds to reach point B from starting point A. Find
(i) the distance covered
(ii) the displacement (iii) the speed.
Answer.(a) When a body moves in a circular path with uniform called uniform circular motion.
(b) Radius = 50 m
Time = 50 s
(i) The distance covered by an athlete A to B i.e., semicircle of the track circumference = 2(3.14)r
circumference-half = (3.14)r
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V. Activity-Based Questions
Question.1. Discuss whether the walls of your classroom are at rest or in motion.
Answer. The walls of the classroom are at rest.

Question.2. • Have you ever experienced that the train in which you are sitting appears to move while it is at rest?
• Discuss and share your experience.
Answer. The train in which we are sitting appears to move while it is at rest, this *we can feel if the vehicles move besides the train.
If one sees any object to be in motion near the train it appears that train is in motion although it is at rest.

Question.3. • Take a metre scale and a long rope.
• Walk from one comer of a basket ball court to its opposite comer along its sides.
• Measure the distance covered by you and magnitude of the displacement.
• What difference would you notice between the two in this case?
Answer. The distance covered by me while walking from one comer of a basketball court to its opposite comer along its sides is more i.e., A to B and B to C —> 2x.
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The magnitude of the displacement is from A to C. Which is much less than the distance travelled.

Question.4. • Automobiles are fitted with a device that shows the distance travelled. Such a device is known as’an odometer. A car is driven from Bhubaneswar to New Delhi. The difference between the final reading and the initial reading of the odometer is 1850 km.
• Find the magnitude of the displacement between Bhubaneswar and New Delhi by using the road map of India.
Answer. To find the magnitude of displacement there are two ways:
• Find the aerial distance from atlas.
• Measure straight distance between two places and convert the measurement as per scale given in the map.

Question.5. • The data regarding the motion of two different objects A and B are given in table below.
• Examine them carefully and state whether the motion of the objects is uniform or non-uniform.
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Answer. Object A travels equal distances in equal intervals of time. Hence A is showing uniform motion.
Object B travel unequal distances in equal intervals of time. Hence B is showing non-uniform motion.

Question.6. • Measure the time it takes you to walk from your house to your bus stop or the school. If you consider that your average walking speed is 4 km/h, estimate the distance of the bus stop or school from your house.
Answer. The time it takes to walk from my house to the school is 30 minutes’—
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Question.7. • At a time when it is cloudy, there may be frequent thunder and lightning. The sound of thunder takes some time to reach you after you see the lightning.
• Can you answer why this happens?
• Measure this time interval using a digital wrist watch or a stop watch.
• Calculate the distance of the nearest point of lightning. (Speed of sound in air = 346 m/s.)
Answer.
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Question.8.In your everyday life you come across a range of motions in which
(a) acceleration is in the direction of motion,
(b) acceleration is against the direction of motion,
(c) acceleration is uniform,
(d) acceleration is non-uniform.
Can you identify one example each of the above type of motion?
Answer.
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Question.9.The time of arrival and departure of a train at three stations A, B and C and the distance of stations B and C from station A are given in the table.
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• Plot and interpret the distance-time graph for the train assuming that its motion between any two stations is uniform.
Answer.
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• As the distance time graph of a train between station A and B; and B and C is a straight line, so the train is moving with a uniform speed between the two stations.

Question.10. Feroz and his sister Sania go to school on their bicycles. Both of them start at the same time from their home but take different time to reach the school although they follow the same route. The table below shows the distance travelled by them in different time.
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Answer.
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Both Feroz and Sania started at 8 am to travel and reach their school, the distance covered by them is 3.6 km.
Feroz reaches the school at 8:20 am and Sania reaches at 8:25 am.
The graph plotted to their motion on distance-time graph shows that the speed of Feroz is more than that of Sania.

Question.11. • Take a piece of thread and tie a small piece of stone at one of its end. Move the stone to describe a circular path with constant speed by holding the thread at the other end as shown in figure.
• Now, let the stone go by releasing the thread.
• Can you tell the direction in which the stone moves after it is released?
• By repeating the activity for a few times and releasing the stone at different positions of the circular path, check whether the direction in which the stone moves remains the same or not.
Answer. When the stone is released. It moves along a straight line, tangential, to the circular path.
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VI. Value-Based Questions

Question.1. A water tanker was completely filled with water. Abhishek saw the driver covering the mouth of the tanker with the lid. He immediately stopped the driver from doing so and told him that the tanker while moving can lose balance and overturn/ topple.
(a) Why will the tanker overturn if its lid is closed?
(b) If the moving tanker with more than half-filled with water, applies sudden brake in which direction will the water fall.
(c) What value of Abhishek is seen in the above case?
Answer. (a) The moving tanker completely filled with water is in inertia of motion, both water and tanker experiences momentum. On applying sudden brakes the tanker will come to rest but the water will continue to remain in motion and hence the tanker will lose the balance and topple.
(b) The water- will fall forward.
(c) Abhishek showed the value of being intelligent, helpful and caring.

Question.2. A car was moving at a speed of 120 km/h on an expressway, suddenly the tyre of the car got punctured and burst. The driver of the car did not apply sudden brakes but he slowed down his vehicle and finally stopped at a road side choosing the appropriate place. All the passengers in the car were shocked but glad with the driver’s decision.
(a) What would have happened if the driver applied sudden brakes?
(b) On applying brakes in which direction would the passengers fall?
(c) What value of driver is seen in this act?
Answer. (a) If the driver would have applied sudden brakes then all the passengers would get hurt and even other vehicles moving on the expressway would have collided with this car from behind.
(b) On applying brakes the passengers would fall in the forward direction.
(c) The driver showed the presence of mind, concern and responsible behaviour.