Question

Assertion :In jumping on sand (or water) the time of contact is increased due to yielding of sand or water so force is decreased and we are not injured. However if we jump on cemented floor the motion stops in a very short interval of time resulting in a large force due to which we are seriously injured. Reason: China wares are wrapped in straw or paper before packing.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

From Newton's second law we know, $\text{Force}\propto \text{Rate of change of momentum}$

$\therefore F\propto \frac{\Delta P}{\Delta t}$, where $\Delta P$ is the change in momentum and $\Delta t$ is the change in time.

If $\Delta t$ is more then $F$ will be less. That is why when a person jumps on the sand, the time of contact will be more and hence the force acting on the person will be less. So he will not be hurt.

Both the assertion and the reason are correct. But the reason is not the correct explanation of the assertion.