A ball is projected upwards from the top of a tower with a velocity 50 ms−1 making an angle 30∘ with the horizontal. The height of tower is 70 m. After how many seconds from the instant of throwing, will the ball reach the ground. ( g=10 ms−2 )
a. 2 s
b. 5 s
c. 7 s
d. 9 s