Question

Assertion: In high jump, it hurts less when an athlete lands on a heap of sand.
Reason: Because of greater distance and hence greater time over which the motion of an athlete is stopped, the athlete experiences less force when lands on the heap of sand.
A) Both assertion and reason are correct and reason is the correct explanation for assertion
B) Both assertion and reason are correct and reason is not the correct explanation for assertion
C) Assertion is correct but the reason is incorrect
D) Assertion is incorrect but the reason is correct

Answer 1

Hint: For this question, we must have good knowledge of Newton’s laws of motion, Momentum, and Impulse. We should consider exactly what happens when a person jumps on a heap of sand from some height and compare the result with the condition that this time, the person is landing on a solid marble floor.

Complete step by step solution:
When a person lands on the heap of sand while performing a high jump, the heap of sand will change its shape according to the force exerted by the person on the heap of sand and the time of contact of the heap of sand and that of the person increases before stopping. But when a person lands on a solid marble floor while performing a high jump, the solid marble will not change its shape because the structure of the marble is rigid and the time of contact of a person with the floor is very less before stopping. In the case of a heap of sand, the impulse generated is less compared to the solid marble floor, and therefore the force experienced by the person when he/she lands on the sand is very less in comparison to that of the solid marble floor.

Hence, option (A) Both assertion and reason are correct and the reason is the correct explanation for the assertion, is the correct answer.

Note: Impulse is defined as the change of momentum per change in time of the event. If the change in time is more, the impulse generated is less, and hence the experienced force will be less and vice versa. So, we can say that impulse is directly proportional to the force.