Question

Two tall buildings face each other and are at a distance of 180 m from each other. With what velocity must a ball be thrown horizontally from a window 55 m above the first building, so that it enters a window 10.9 m above the ground in the second building?
1. 10 m/sec
2. 30 m/sec
3. 60 m/sec
4. None

Answer 1

Correct Answer - Option 3 : 60 m/sec

Vertical downward distance covered by the ball = 55 – 10.9 = 44.1 m

Initial vertical velocity of the ball, u_y = 0

\(\begin{array}{l} s = {u_y}t + \frac{1}{2}g{t^2}\\ \Rightarrow 44.1 = 0 + \frac{1}{2} \times 9.8 \times {t^2}\\ \Rightarrow t = 3\;sec\; \end{array}\)

Required horizontal velocity, \({v_{horizontal}} = \frac{{180}}{3} = 60\;m/sec\)