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