Question

Assertion :A stone dropped from a height, moves with constant velocity. Reason: Time of descent is directly proportional to the square root of the initial velocity of the body.

• 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 D Both Assertion and Reason are incorrect

Initial speed of the stone is zero i.e. $u=0$

As an acceleration due to gravity $\left(g\right)$ acts on the stone is downward direction, thus the stone accelerates with time which results in the change of velocity of the stone.

Hence the stone does not move with constant velocity.

Using $S=ut+\frac{1}{2}g{t}^2$

Or $S=0+\frac{1}{2}g{t}^2$

$⟹$ $t=\sqrt{\frac{2S}{g}}$

Thus time of descent depends only on the height from which the stone is dropped.

Hence both assertion and reason are incorrect.