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

Options

A. 6s
B. 6.5s
C. 7s
D. 7.5s

Answer

C

Explanation

Total height to fall
`h=(1)/(2)"gt"^(2)=(1)/(2)xx10xx(5)^(2)=125m`
In first 3 sec.
`s_(1)=(1)/(2)"gt"_(1)^(2)=(1)/(2)xx10(3)^(2)=45m`
Now remaining height to fall `therefore s_(2)=h-s_(1)=125-45=80m`
`t_(2)=sqrt((2s_(2))/(g))=sqrt((2xx80)/(10))=4` sec
`t=t_(1)+t_(2)=3+4=7` sec