Newton’s laws of Motion
CBSE 9 Worksheet
1. Why does a passenger in a car feel a backward push when a slow moving or stationary car accelerates
suddenly?
2. Why does a passenger in a car get moved towards the left side when a car takes a sharp turn towards
right?
3. Name the property of bodies by virtue of which they resist a change in their state of rest or of uniform
motion.
4. Name the physical quantity which is measured/ determined by the rate of change of momentum.
5. Write the net force acting on a bus, of mass 2000 kg, moving with a uniform velocity of 60 km/h.
6. In the collision between a heavier body and a lighter body, if the force experienced by the heavier body
is F1 and that by the lighter body is F2, write the relation between F1 and F2.
7. A 1000kg car is stationary on a road. The road applies 2000N of frictional force on that car when it is in
motion.
a. How much of constant force should the engine generate so that the car accelerates at a rate of 2m/s 2.
Draw force diagram for the car for this situation.
[4000 N]
b. For how many seconds will the engine have to generate that force so that the car reaches a speed of
10m/s? [5s]
c. As soon as the car reaches a speed of 10 m/s the amount of force applied is changed in a way that the
car speed stays constant of 10 m/s. How much force should be generated by the engine to achieve
this condition? Explain your answer. Also depict this situation using a force diagram. [2000N]
d. Now, the car moves at the constant velocity of 10m/s for 10 seconds. How much distance will it
cover? [100m]
e. At the end of 10 sec mentioned in part d, the engine’s force increases to 3000N and stays so for 5
seconds.
i. What will be the net force on the car now? Draw force diagram showing that. [1000N]
ii. How much distance will the car travel in this duration?
[72.5m]
iii. What will be its final speed?
[15m/s]
f. After this, the engine stops generating force. How much time will the car take to come to a stop?
[7.5s]
g. Sketch a rough Velocity-Time graph showing the relevant velocity and time values on the axis but
the axis need not be drawn to scale.
h. Sketch a rough Displacement-Time graph (not to scale) showing the relevant displacement and time
values on the axis but the axis need not be drawn to scale.
8. An object of mass 100 kg is accelerated uniformly from a velocity of 5 m/s to v m/s in 6 s by a force of
50N. Find the value of v.
[8 m/s]
9. (i) A heavy and a light object have same momentum. Which of these is travelling faster?
(ii) State the law of conservation of momentum. Give one example.
10. A construction worker on top of a 80m high building dropped his helmet. After how long, since the
moment when he dropped it, will the worker hear the sound of the helmet striking the ground? Speed of
sound in air is 330m/s and acceleration due to gravity is 10m/s 2. Ignore the effect of air resistance.
[Ans: 4.24 sec]
11. From a rifle of unknown mass, a bullet of mass 50 g is fired with an initial velocity of 35 m/s. This
causes the rifle to recoil with a velocity of 350 cm/s. Find the mass of the rifle.
[Ans:
5kg]
12. A hockey ball of mass .2 Kg travelling at 10 ms -1 is struck by a hockey stick so as to return it along its
original path with a velocity at 2 ms-1 . Calculate the change of momentum occurred in the motion of the
hockey ball by the force applied by the hockey stick.
[Ans: 2.4 kg ms-1]
Forces Worksheet
9 CBSE
Very Short Questions Type
1. During the game of table tennis, if the ball hits a player it does not hurt him. On the other hand when a
fast moving cricket ball hits a spectator it may hurt him. State reason.
2. Define the first law of motion.
3. Why does a backseater move forward when a fast moving bike is stopped suddenly?
4. When a carpet is beaten with a stick it releases dust. Explain why.
5. Explain why some of the leaves may get detached from a tree if we vigorously shake its branch?
6. An athlete always runs some distance before taking a jump. Why?
7. Name the physical quantity that measures inertia. State its SI unit.
8. State the relation between the momentum of a body and the force acting on it.
9. What is the mathematical formula and SI unit of momentum?
10. What is the momentum of a body of mass 5 kg moving with a velocity of 0.20 m/s.
11. A body of mass 25 kg has a momentum of 125 kg m/s. calculate the velocity of the body.
12. What force would be needed to produce an acceleration of 4 m/s2 on a ball of mass 6 kg?
13. State Newton’s third law of motion.
14. An object of mass 100 kg is accelerated uniformly from a velocity of 5 ms-1 to 8 ms-1 in 6 s. Calculates
the initial and final momentum of the object. Also find the magnitude of force exerted on the object.
[500 kgm/s, 800kgm/s, 50N]
15. Out of the four physical quantities associated with the motion of an object viz force, velocity,
acceleration and momentum which one remains constant for all bodies large or small, undergoing a free
fall?
16. How are action – reaction forces related in magnitude and direction?
1.
2.
3.
4.
5.
6.
7.
8.
Short Answer Type questions
There are three solids made up of aluminium, steel and wood, of the same shape and same volume.
Which of them would have highest inertia?
Two friends on roller – skates are standing 5 m apart facing each other. One of them throws a ball of 2
kg towards the other, who catches it. How will this activity affect the positions of the two? Explain your
answer.
Give reason and give the law related to these statements:
(a) It is easier to push an empty box than to push the box full of books.
(b) It is difficult for a fireman to hold a hose which ejects large amount of water with high velocity.
It is necessary to run along with the moving bus in the same direction of the bus, after alighting from the
bus. Give reasons.
(a) Name the force that keeps the object moving in a circular path with constant acceleration.
(b) Which direction will this object move if this force is removed?
Which of the following has more inertia? Give reason for your answer:
(i)
A bicycle and a train
(ii)
A rubber ball and a stone of the size.
(iii)
A ten rupee coin and a one rupee coin.
(iv)
A bicycle or a truck.
Two objects A and B of same masses but velocities of V and 3 V respectively are in motion.
(a) Which object will have larger momentum?
(b) Give reason to support your answer ‘a’.
While playing football, the goalkeeper did not get sufficient time to stop a fast ball shot towards him.
Why did he hurt his hand while doing so?
9. The hand gets hurt while punching a wall. Why?
10. (i) Describe and explain how rowing causes a boat to move.
(ii) Why action and reaction do not cancel each other?
11. What is the effect of force, when it is applied in the following cases?
a) Balloon is pressed from opposite sides.
b) A ball coming towards the bat is hit with a bat. What is the effect on the ball?
c) Spring is compressed.
12. If you are trying to push a heavy box on a horizontal surface, list various forces acting on the box. State
the condition under which this box will start sliding on the surface. How will the magnitude of applied
force required to move the box change if:
a) Weight of the box is increased?
b) The surface on which the box is placed is made more rough?
13. A pile of carom coins is hit with a fast sliding striker. What happens to the carom coins and why?
14. Define SI unit of force. How much net force is required to accelerate a 1000 kg car at 4 m/s2? [4000N]
Numerical Problems
1. Find the change in momentum of a car weighing 1500 kg when its speed increases from 36 km/h to 72
km/h.
[15000 kgm/s]
2. A force of 2 N acting on a body changes its velocity uniformly from 2 m/s to 5 m/s in 10 s. calculate the
mass of the body. [6.67N]
3. During tug of war, a rope of 10 kg, that is initially stationary, is being pulled by team A with a force of
1800N and by team B with a force of 1820N. In which direction will it move and with how much
acceleration? How much will the rope move in first 1 second?
[2m/s2, 1m]
4. If you apply a net force of 3 N on 0.1 kg box, what is the acceleration of the box
(a) 3 m/s2
(b) 30 m/s2
(c) 0.2 m/s2
(d) 10 m/s2
[Ans: b]
5. A body of mass 1 kg undergoes a change of velocity of 4m/s in 4s what is the force acting on it? [1N]
6. A stone released from the top of a tower of height 19.6 m. calculate its final velocity just before
touching the ground. Take value of g as 9.8 m/s2. [20m/s]
7. A particle of 10 kg is moving in a constant acceleration 2m/s2 starting from rest. What is its momentum
and velocity per the table given below
S.No.
Time taken from start
Momentum
Velocity
1
1sec
2
1.5 Sec
3
2 sec
4
2.5 sec
[20 kgm/s,2m/s, 30 kgm/s,3m/s, 40 kgm/s,4m/s, 50 kgm/s,5m/s]
8. If a net force of 7 N was constantly applied on 400 g object at rest, how long will it take to raise its
velocity to 80 m/s?
a) 0 s
b) 2.23 s
c) 3.47 s
d) 4.57 s
Ans: d
9. A sedan car of mass 200kg is moving with a certain velocity. It is brought to rest by the application of
brakes, within a distance of 20m when the average resistance being offered to it is 500N.What was the
velocity of the motor car?
[10m/s]
10. A driver accelerates his car first at the rate of 4 m/s 2 and then at the rate of 8 m/s 2 . Ignoring friction,
calculate the ration of the forces exerted by the engines in the two situations?
[old F: new F = 1:2]
11. An object of mass 10 g is sliding with a constant velocity of 2 m/s on a frictionless horizontal table. The
force required to keep the object moving with the same velocity is
(a) 0 N
(b) 5 N
(c) 10 N
(d) 20 N
Ans: a
12. A cricket ball of mass 0.20 kg is moving with a velocity of 1.2m/s. Find the average force applied by the
player if he is able to stop the ball in 0.10s?
[2.4 N]
13. A car starts from rest and acquire a velocity of 54 km/h in 2 sec. Find (i) the acceleration (ii) distance
travelled by car assume motion of car is uniform iii) If the mass of the car is 1000 Kg, what is the force
acting on it?
[7.5 m/s2, 15m, 7500N]
14. From a rifle of mass 5 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m/s. Calculate the
initial recoil velocity of the rifle.
[0.35 m/s]
15. An object of mass 1 kg travelling in a straight line with a velocity of 10 m/s collides with, and sticks to a
stationary wooden block of mass 5 kg. Then they both move off together in the same straight line.
Calculate the total momentum just before the impact and after the impact. Also calculate the velocity of
the combined object.
[1.67 m/s]
16. Two objects of masses of 100 gm and 200 gm are moving in along the same line and in same direction
with velocities of 2 ms-1 and 1 ms-1 respectively. They collide and after collision, the first object moves
at a velocity of 1.6 ms-1. Determine the velocity of the second object.
[1.2 m/s]
17. A stationary object of mass 1 kg acquires a speed of 10 m/s when pushed forward. What is the change of
momentum of the object?
[10kgm/s]
18. A gun of mass 3 kg fires a bullet of mass 30 g. the bullet takes 0.003 s to get pushed by the gun’s spring
and acquires a velocity of 100 m/s. calculate the force exerted on gunman due to recoil of the gun.
[1000N]
19. The velocity–time graph of a car is given below. The car weighs 1000 kg.
What is the net force acting on the car for following
durations:
i) A to B
[7500 N]
ii) B to C
[0 N]
iii) C to D
[-15000 N]
If the amount of frictional force is 1000 N all though out the
cars journey, find the amount of force generated by the
engine or applied by the brakes in the three time durations:
a) A to B
[engine: 8500 N]
b) B to C
[engine: 1000N]
c) C to D
[brakes: 14000N]
Sketch force diagrams of the car for each of the three parts
of the journey.