Question

23.A stone dropped from a certain height can reach the ground in 5 s.<br />It is stopped after 3 seconds of its fall and then allowed to fall<br />again. Find the time taken by the stone to reach the ground for the<br />remaining distance.<br />A. 2 s<br />B, 4 s<br />C. 6 s<br />D. 8s<br />E. 10 s​

Answer 1

Explanation:

First let us find the height above the ground from which the stone is dropped.

It is given that the stone reaches the ground in 5s.

Hence the height h = (1/2)×g×t2 = (1/2)×10×5×5 = 125 m( g is assumed as 10 m/s2 )

Vertical distance travelled in initial 3 s, h1 = (1/2)×10×3×3 = 45 m

remaining distance h2 = 125-45 = 80 mtime taken t to travel remaining distance is given by, 80 = (1/2)×10×t2 , we get t = 4 s

Hence total time = 4+3 = 7 s