Multiple Choice Questions
1. Which of the following statement 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 the earth
(d) A force is always acting on it
Ans. (c) It always goes away from the earth
Explanation: To move away from the earth, an object needs the acceleration which is more than acceleration due to gravity. Only moving on a straight path is not enough for an object to escape the gravitation of the earth.
2. According to the third law of motion, action and reaction
(a) always act on the same body
(b) always act on different bodies in opposite directions
(c) have same magnitude and directions
(d) act on either body at normal to each other
Ans. (b) always act on different bodies in opposite directions
Explanation: Action and reaction act on different bodies but in opposite directions. They have the same magnitude.
3. A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goal keeper to
(a) exert larger force on the ball
(b) reduce the force exerted by the ball on hands
(c) increase the rate of change of momentum
(d) decrease the rate of change of momentum
Ans. (b) reduce the force exerted by the ball on hands
Explanation: Pulling the hand backwards allows enough time to reduce the momentum of the ball. This helps in reducing the force exerted by the ball on hands.
4. 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 its state of motion
(d) to decelerate due to friction
Ans. (c) to resist any change in its state of motion
Explanation: Inertia is the property because of which an object resists any change in its state of motion.
5. A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is
(a) accelerated
(b) uniform
(c) retarded
(d) along circular tracks
Ans. (a) accelerated
Explanation: Had the motions of the train been uniform, the coin would have fallen in his hand. Had the motion been retarded, the coin would have fallen ahead of him. So, motion is accelerated.
6. An object of mass 2 kg is sliding with a constant velocity of 4 ms–1 on a frictionless horizontal table. The force required to keep the object moving with the same
velocity is
(a) 32 N
(b) 0 N
(c) 2 N
(d) 8 N
Ans. (b) 0 N
Explanation: Since no friction is opposing the motion, hence no force is required to keep the object in uniform motion.
7. Rocket works on the principle of conservation of
(a) mass
(b) energy
(c) momentum
(d) velocity
Ans. (c) momentum
8. A water tanker 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
(a) move backward
(b) move forward
(c) be unaffected
(d) rise upwards
Ans. (b) move forward
Explanation: On sudden application of brake, the tanker would come to rest but water would remain in motion. Due to this, the water in the tank would move forward.
