A ball is thrown vertically upwards from the ground and a student gazing out of the window sees it moving upward past him at 10ms The window is at 15m above the ground level. The velocity of ball 3s after it was projected from the ground is `[Take g=10ms^(-2)]`

Options

A. `10m//s`, up
B. `20ms^(-1)`, up
C. `20ms^(-1)`, down
D. `10ms^(-1)`, down

Answer

D

Explanation

Total height `h=15 + u^2/(2g) =15+((10)^2)/(2xx10) or h=20m`
Initial velocity `u=sqrt(2gh)=sqrt(2xx10xx20)=20 m//s`
Now applying `v=u+at`, we have
`v=(+20)+(-10)(3)=-10m//s`
`:.` Velocity is 10 m/s downwards