A body falls freely from a height of 125 m `(g=10 m//s^(2))`. After 2 sec gravity ceases to act find time taken by it to reach the ground?

Explanation

Distance covered in 2s under gravity
`S_(1)=(1)/(2)g t^(2)=(1)/(2)(10)(2)^(2)=20m`
Velocity at the end of 2s
`V=g t=10 xx2=20 m//s`
Now at this instant gravity ceases to act, there after velocity becomes constant. The remaining distance which is `125-20=105m` is covered by body with constant velocity `20 m//s` time taken to cover 105 m with constant velocity
is given by
`t_(1)=(S)/(V)impliest_(1)=(105)/(20)=5.25s`
Total time taken `=2+5.25=7.25s`