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

Answer

C

Explanation

by `s_(y)=u_(y)t+(1)/(2)a_(y)t^(2)`
`rArr h=-u sin 30^(@)t+(1)/(2)"gt"^(2)`
`rArr 70=-50xx(1)/(2)t+(1)/(2)xx10t^(2)rArr t=7` sec