Question

A ball is projected upwards from the top of the 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 the ball will strike the ground?

• A. 3 sec
• B. 5 sec
• C. 7 sec
• D. 9 sec

Answer 1

Answer: (C)

7 sec

Answer 2

$\overline{Y}$ = ${\overline{v}}_{y}t + \frac{1}{2}{\overline{a}}_{y}t^{2}$

70 = –(50 sin 30^C) t + $\frac{1}{2}$×10 × t²

70 = –25 t + 5t²

or t²–5t –14 = 0 ̃ t = –2sec

or t = 7sec. (–ve time is not possible)