Q. Two balls are dropped to the ground from different heights. One ball is dropped $2s$ after the other but they both strike the ground at the same time. If the first ball takes $5s$ to reach the ground, then the difference in initial heights is $(g = 10\ ms^{- 2})$
A) $20m$
B) $80m$
C) $170m$
D) $40m$
Explanation
(b) $S_{2} = \frac{1}{2}{gt}_{2}^{2} = \frac{10}{2} \times (3)^{2} = 45\ m$
$S_{1} = \frac{1}{2}gt_{1}^{2} = \frac{10}{2} \times (5)^{2} = 125\ m$
$\therefore S_{1} - S_{2} = 125 - 45 = 80\ m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.