MCQ : Science (Physics) class 9 Forces and Laws of Motion Chapter 9
1. What is the momentum of an object of mass m, moving with a velocity v ?
(i) (mv)2
(ii) mv2
(iii) 1/2 (mv)2
(iv) mv
Answer:
(iv) mv
2. Force is the rate of change of
(i) momentum
(ii) velocity
(iii) displacement
(iv) acceleration
Answer:
(a) momentum
3. The magnitude of the impulse on the object is
(i) 0 N s
(ii) 107 dyne s
(iii) 1 N s
(iv) 10 N s
Answer:
(iv) 10 N s
4. The average force acted on the object is
(i) 0.1 N
(ii) 0.003 N
(iii) 3.3 N
(iv) 3 N
Answer:
(iii) 3.3 N
5. In SI system, the gravitional unit of force is
(i) Kg ms-2
(ii) kgf
(iii) m/s
(iv) meter
Answer:
(ii) kgf
6. The unit of measuring the momentum of a moving body is
(i) m/s
(ii) kg m/s
(iii) Kg m/s2
(iv) N m2/ kg2
Answer:
(ii) kg m/s
7. A man wearing a bullet proof vest stands on roller skates. The total mass is 80 kg. A bullet of mass 20 g is fired at 400 m/s. It is stopped by the vest and falls to the ground. What is then the velocity of the man ?
(i) 1 m/s
(ii) 0.1 m/s
(iii) 0.01 m/s
(iv) 0 m/s
Answer:
(ii) 0.1 m/s
8. A passenger in a moving train tosses a coin which falls behind him. Observing this statement what can you say about the motion of the train ?
(i) accelerated
(ii) reatrded
(iii) a long circular tracks
(iv) uniform
Answer:
(i) accelerated
9. The speed of a car weighing 1500 kg increases from 36 km/h to 72 km/h uniformly. What will be the change in momentum of the car ?
(i) 15000 kg km/h
(ii) 15000 kg m/s
(iii) 54000 kg m/s
(iv) 54000 g m/s
Answer :
(ii) 15000 kg m/s
10. Which of the following situations involves the Newton's second law of motion ?
(i) a force can stop a lighter vehicles as well as a heavier vehicle which are moving
(ii) a force exerted by a lighter vehicle on collision with a heavier vehicle results in both the vehicles coming to stand still
(iii) a force can accelerate a lighter vehicle more easily than a heavier vehicle which are moving
(iv) a force exerted by the escaping air from a balloon in the downward direction makes the balloon to go upwards
Answer:
(iii) a force can accelerate a lighter vehicle more easily than a heavier vehicle which are moving
11. When a balloon held between the hands in pressed, its shape changes. This happens because
(i) balanced forces act on the balloon
(ii) unbalanced forces act on the balloon
(iii) frictional forces act on the balloon
(iv) gravitional force act on the balloon
Answer:
(i) balanced forces act on the balloon
12. The seat belts are provided in the cars so that if the car stops suddenly due to an emergency braking, the persons sitting on the front seats are not thrown forward violently and saved from getting injured. Can you guess the law due to which a person falls in forward direction on the sudden stopping of the car ?
(i) Newton's first law of motion
(ii) Newton's second law of motion
(iii) Newton's third law of motion
(iv) Newton's law of gravition
Answer:
(i) Newton's first law of motion
13. A water tank filled up to 2/3 of its height is moving with a uniform speed. On sudden application of the brake, the water in the tank would
(i) move backward
(ii) move forward
(iii) come to the rest
(iv) be unaffected
Answer:
(ii) move forward
14. An object of mass 2 Kg is sliding with a constant velocity of 4 m/s on a friction less horizontal table. The force required to keep the object moving with the same velocity is
(i) 32 N
(ii) 0 N
(iii) 2 N
(iv) 8 N
Answer :
(ii) 0 N
15. A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goalkeeper to
(i) exert large force on the ball
(ii) increases the force exerted by the ball on hands
(iii) increases the rate of change of momentum
(iv) decreases the rate of change of momentum
Answer:
(iv) decreases the rate of change of momentum
16. Which of the following statements are not correct for an object moving along a straight path in an accelerated motion ?
(i) its speed keeps changing
(ii) its velocity always changes
(iii) it always goes away from the Earth
(iv) a force is always acting on it
Answer:
(iv) a force is always acting on it
17. According to the third law of motion , action and reaction
(i) always act on the same body
(ii) always act on different bodies in opposite directions
(iii) have same magnitude and directions
(iv) act on either body at normal to each other
Answer:
(ii) always act on different bodies in opposite direction
18. The inertia of an object tends to cause the object
(i) to increase its speed
(ii) to decrease its speed
(iii) to resist any change in its state of motion
(iv) to decrease due to friction
Answer:
(iii) to resist any change in its state of motion
19. A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is
(i) accelerated
(ii) uniform
(iii) retarded
(iv) along circular tracks
Answer:
(i) accelerated
20. Rocket works on the principal of conservation of
(i) mass
(ii) energy
(iii) momentum
(iv) velocity
Answer:
(iii) momentum