A ball is projected upwards from the top of a tower with a velocity `50ms^-1` making an angle `30^@` with the horizontal. The height of tower is 70m. After how many seconds from the instant of throwing, will the ball reach the ground. `(g=10 ms^-2)`

Options

A. 2 s
B. 5 s
C. 7 s
D. 9 s

Answer

C

Explanation

Using `s = ut + 1/2 at^2` in vertical direction
`:. -70 = (50 sin 30^@)t + 1/2 (-10)t^2`
On solving this equation, we get
`t = 7s`.