Q. A balloon is rising vertically up with a velocity of $29\ {ms}^{- 1}.$ A stone is dropped from it and it reaches the ground in 10 s. The height of the balloon when the stone was dropped from it is $\left( g = 9.8\ {ms}^{- 2} \right)$
A) 400 m
B) 150 m
C) 100 m
D) 200 m
Explanation
(d) For a stone which is thrown downwards from a balloon rising upwards, the equation of motion is
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ h = - ut + \frac{1}{2}gt^{2}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = - 29 \times 10 + \frac{1}{2} \times 9.8 \times (10)^{2}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = - 290 + 490 = 200\ m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.