Question

21. A stone is dropped from a certain height which can reach the ground in 5 sec. It is stopped
after 3 sec. of its fall and then is again is released. The total time taken by the stone to reach
the ground will be​

Answer 1

Answer:

8 seconds

Explanation:

because 5+3=8

Answer 2

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 m

time 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