A ball is projected upwards from the top of a tower with velocity 50 m`s^(-1)` making an angle of 30° with the horizontal. If the height of the tower is 70 m, after what time from the instant of throwing, will the ball reach the ground (g = 10 `ms^(-2)` ):

Options

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

Answer

C

Explanation

Here -`u_(y)=usintheta=50xx1/2=25ms^(-1)`
`:.h=-70m,a=-10m//s^(2)`
Using `h=ut + 1/2g t^(2)`
`-70=25t - 5t^(2)`
Solving this, we get t=7s