The velocity of a freely falling body when it strikes the ground is directly proportional to the square of the time taken by it to strike the ground. It takes 5 seconds to strike the ground, with a velocity of 10 m/sec. If it strikes the ground with the velocity of 40 m/sec, then for how long would it have travelled ?

Options

A. ` 7.5` sec
B. ` 2.5` sec
C. 10 sec
D. 20 sec

Answer

C

Explanation

(i) `V_(1)/V_(2)=t_(1)^(2)/t_(2)^(2)`.(Apply the concept of variation).
(ii)Given that `V/t_(2) = k` (where k is constant).
(iii) `V_(1)/t_(1)^(2) = V_(2)/t_(2)^(2)`.