A ball is thrown vertically upwards with a velcotiy of `20 ms^(-1)` from the top of a multi-storey building. The height of the point fromwher the ball is thrown if 25m from the ground. (a) How high the ball will rise ? And (b) how long will it be before the ball hits the ground ? Take. `g=10 ms^(-2)`.

Options

A. 10 m
B. 15 m
C. 45 m
D. 25 m

Answer

C

Explanation

Taking vertical upward motion of the ball upto highest point.
Here, u = `20 m s^(-1)`
v = 0 (At highest point velocity is zero)
`a = -g = -10 m s^(-2)`
As `v^(2) = u^(2) + 2aS`
`0 = (20)^(2) + 2(-10)(S)` or `S = 20 xx 20/20` = 20 m