Q. A ball is thrown vertically upwards with a velocity of $25\ ms^{- 1}$ from the top of a tower of height $30\ m$. How long will it travel before it hits ground
A) $6s$
B) $5s$
C) $4s$
D) $12s$
Explanation
(a) $S = ut + \frac{1}{2}gt^{2}$
$30 = - 25t + \frac{10}{2}t^{2}$ or $t^{2} - 5t - 6 = 0$
Or $(t - 6)(t + 1) = 0$ Take positive root
$\therefore t = 6\ \sec$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.