Q. A ball is dropped from top of a tower of $100m$ height. Simultaneously another ball was thrown upward from bottom of the tower with a speed of $50\ m/s$ ($g = 10\ m/s^{2}$). They will cross each other after
A) $1s$
B) $2s$
C) $3s$
D) $4s$
Explanation
(b) $h_{1} = \frac{1}{2}gt^{2},\ h_{2} = 50t - \frac{1}{2}gt^{2}$
Given $h_{1} + h_{2} = 100\ m$
$\Rightarrow 50t = 100 \Rightarrow t = 2\ sec$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.