## MCQ Questions for Class 9 Science: Ch 9 Force and Laws of Motion 1. A plate, a ball and a child all have the same mass. The one having more inertia is the
(a) plate
(b) ball
(c) child
(d) All have equal inertia
► (d) All have equal inertia

2. The inertia of an object tends to cause the object
(a) to increase its speed
(b) to decrease its speed
(c) to resist any change in the state of rest or of motion
(d) to decelerate due to friction
► (c) to resist any change in the state of rest or of motion

3.  The rate of change of momentum with respect to time is measured in
(a) kg ms-2
(b) kg ms-1
(c) kg m
(d) kg
► (a) kg ms-2

4. When unbalanced forces act on a body, the body:
(a) Must move with uniform velocity
(b) Must remain at rest
(c) Must experience acceleration
(d) Must move in a curved path
► (c) Must experience acceleration

5. A man throws a ball weighing 200 g vertically upwards with a speed of 10m/s. Its momentum at the highest point of its flight will be:
(a) 2 kg. m/s
(b) 2000 kg.m/s
(c) Insufficient data to find the momentum.
(d) zero
► (d) zero

6. Quantitative expression of force is given by:
(a) Newton’s second law of motion.
(b) Newton’s third law of motion.
(c) Newton’s first law of motion.
(d) Newton’s law of gravitation.
► (a) Newton’s second law of motion.

7. Find the time taken by a body of mass 16 kg to come to rest from a uniform velocity of magnitude 10 m/s, when a force of 4N is applied continously
(a) 20 s
(b) 30 s
(c) 40 s
(d) 50 s
► (c) 40 s

8.  The S.I. unit of force is
(a) Newton-metre
(b) Newton
(c) Newton per second
(d) Newton per square metre
► (b) Newton

9. A force of ‘P* N acts on a particle so as to accelerate it from rest to a velocity 'v' m/s. The force 'P’ is then replaced by ‘Q’ N which decelerates it to rest.
(a) P may be equal to Q
(b) P must be equal to Q
(c) P must be unequal to Q
(d) none of these
► (a) P may be equal to Q

10. If the force acting on the body is zero. Its momentum is:
(a) Zero
(b) Constant
(c) Infinite
(d) None of the above
►(b) Constant

11. When a force is exerted on an object, it can change its:
(a) State
(b) Position
(c) Shape
(d) All the above
► (d) All the above

12. What force can change the velocity of a body of mass 1kg from 20 m/s to 30m/s in 2 seconds?
(a) 10 N
(b) 15 N
(c) 5 N
(d) 25 N
► (c) 5 N

13.One way that you can recognize that a force is acting on an object:
(a) is to note any change in the objects state of motion.
(b) is to determine its mass at different locations.
(c) is to measure the instantaneous velocity of a moving object.
(d) A and C
► (a) is to note any change in the objects state of motion.

14. 1-kg object is lying on the ground. An unbalanced force of magnitude 1 N is applied to the object. Which of these options explains the motion of the object as a result of the acting force?
(a) The object will accelerate in the direction of the applied force.
(b) The object will accelerate in a direction perpendicular to the applied force.
(c) The object will decelerate in the direction of the applied force.
(d) The object will remain at rest
► (a) The object will accelerate in the direction of the applied force.

15. When a 12 N force acts on 3 kg mass for a second, the change in velocity is (in m/s)
(a) 36
(b) 4
(c) 2
(d) 18
► (b) 4

16.  A passenger in a moving train tosses a coin which falls behind him. It means that the motion of the train is
(a) accelerated
(b) uniform
(c) retarded
(d) along circular tracks
► (a) accelerated

17. Force is defined as
(a) change in momentum
(b) rate of change of momentum
(c) the quantity that opposes inertia
(d) the quantity that keeps the velocity constant
► (b) rate of change of momentum

18. A force is defined as a
(a) Fall
(b) Pull
(c) Push or Pull
(d) Push
► (c) Push or Pull

19. What is the momentum of a body of mass 2m and velocity v/2?
(a) mv/4
(b) mv
(c) 2mv
(d) mv/2
► (b) mv

20. Two equal masses m each moving in the opposite direction with the same speed v collide and stick to each other. The velocity of the combined mass is
(a) v
(b) 2v
(c) v/2
(d) zero
► (d) zero

21. In high jump competition the athlete is made to fall on a cushioned bed to:
(a) To decrease his momentum fast.
(b) Make him stop quickly.
(c) Increase the time to stop.
(d) Make him sleep comfortably.
► (c) Increase the time to stop.

22. Momentum of a body of mass 0.5 kg moving with a speed of 10 m/s is​
(a) 2.5 kg.m/s
(b) 5 kg.m/s
(c) 0.5 kg.m/s
(d) 50 kg.m/s
► (b) 5 kg.m/s

23. An object of mass of 2 kg is sliding with a velocity of 4 ms-1 on a frictional horizontal surface. The retarding force necessary to stop the object in 1 second is
(a) 2 N
(b) 4 N
(c) 8 N
(d) 0 N
► (c) 8 N

24. The acceleration of an object is
(a) inversely proportional to its mass
(b) directly proportional to the applied force
(c) resisted by inertia
(d) all of the above
► (d) all of the above

25. Which of the following has the largest momentum?
(a) A cat running down the street
(b) A pickup truck travelling down the highway.
(c) A large truck parked in a parking lot.
(d) A car parked in a parking lot.
► (b) A pickup truck travelling down the highway.

26. According to Newton’s third law of motion, action and reaction
(a) always act on the same body
(b) always act on different bodies in opposite direction
(c) have same magnitudes and direction
(d) act on either body at normal to each other
► (b) always act on different bodies in opposite direction

27. Which one of the following statements is not correct for an object moving along a straight path in an accelerated motion?
(a) Its speed keeps changing
(b) Its velocity always changes
(c) It always goes away from earth
(d) A force is always acting on it
► (c) It always goes away from earth

28. Change in momentum when a car weighing 700kg changes its speed from 100m/s to 200 m/s is:
(a) 14000 kg.m/s
(b) 10500000 kg.m/s
(c) 21000000 kg.m/s
(d) 70000 kg.m/s
► (d) 70000 kg.m/s

29. When balanced forces act on a body, the body:
(a) Must remain in its state of rest
(b) Must continue moving with uniform velocity, if already in motion
(c) Must experience some acceleration
(d) Both (A) and (B)
► (d) Both (A) and (B)

30. If an object moves with a uniform velocity we can conclude that
(a) there is no force acting on the body
(b) no unbalanced force acts on it
(c) an unbalanced force acts on the body
(d) it has uniform acceleration
► (b) no unbalanced force acts on it

31. The acceleration of an object is inversely proportional to:
(a) Force.
(b) Momentum.
(c) Mass.
(d) Velocity.
► (c) Mass.

32. Find the time for which a force of 1kgwt acts on a body of mass 1 kg moving with a uniform speed of 4m/s to stop the body.
(a) 0.8 s
(b) 0.2 s
(c) 0.6 s
(d) 0.4 s
► (d) 0.4 s

33. __________ is a force, which always opposes the motion of one body over the other body in contact with it
(a) Gravitational force
(b) Reaction force
(c) Normal force
(d) Frictional force
► (d) Frictional force

34. An object of mass 20 kg is moving with a velocity of 10 m/s. Its momentum will be:
(a) 2000 kg.m/s
(b) 20 kg.m/s
(c) 2 kg.m/s
(d) 200 kg.m/s
► (d) 200 kg.m/s

35.  When the driver of a fast moving car suddenly applies brakes, the passengers in the car:
(a) fall backward
(b) fall forward
(c) are not affected
(d) none of the above
► (b) fall forward

36. A force of magnitude' F' acts on a body of mass 'm'. The acceleration of the body depends upon:
(a) Volume of body
(b) Density of body
(c) Area of body
(d) Mass of body
► (d) Mass of body