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
Soln:
Answer is (c) It always goes away from the earth
Explanation:
To move away from earth Object’s acceleration should be more than the acceleration due to gravity. To escape from gravity only moving along a straight path is not enough hence option (c) is a wrong statement.
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 the same magnitude and directions (d) act on either body at normal to each other.
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
Soln:
Answer is (b) always act on different bodies in opposite directions
Explanation:
Newton’s third law states that “For every action, there is an equal and opposite reaction”. Hence answer is b)
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
Soln:
Answer is (b) reduce the force exerted by the ball on hands
Explanation:
Pulling hands backwards will help goalkeeper to reduce the momentum of the ball which in turn reduces the force of the ball exerted on goalkeeper’s 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
Soln:
Answer is (c) to resist any change in its state of motion
Explanation:
Inertia is the property which resists the state of motion of an object. The object remains in its existing state of rest or uniform motion in a straight line unless that state is changed by an external force.
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
Soln:
Answer is (a) accelerated
Explanation:
If the motion of the train is uniform the coin would have fallen in his hand. If the motion is retarded coin would have fallen ahead of him. Since the coin falls behind the person motion of the train is accelerated.
6. An object of mass 2 kg is sliding with a constant velocity of 4 m/s 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
Soln:
Answer is (b) 0 N
Explanation:
Here the friction is opposing the force hence no force is required to keep the object in uniform motion. Hence, the answer is 0 N.
7. Rocket works on the principle of conservation of
(a) mass
(b) energy
(c) momentum
(d) velocity
Soln:
Answer is (c) momentum
Explanation:
The velocity of hot gases coming out of the rocket provided large momentum in the opposite direction which makes the rocket move upwards. Here the conservation of momentum takes place.
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
Soln:
Answer is (b) move forward
Explanation:
On applying brakes water tanker comes to rest but water will be in motion this makes the water to come forward.
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