Q. From a balloon rising vertically upwards at $5m/s$ a stone is thrown up at $10\ m/s$ relative to the balloon. Its velocity with respect to ground after $2\ s$ is (assume $g = 10m/s^{2}$)
A) $0$
B) $20\ m/s$
C) $10\ m/s$
D) $5\ m/s$
Explanation
(d) Initial velocity of balloon with respect to ground
$v = 10 + 5 = 15\ m/sec$ upward
After 2 seconds its velocity, $v = u - gt$
$= 15 - 10 \times 2 = - 5\ m/sec = 5\ m/sec$ (downward)
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.