Q. An isolated particle of mass $m$ is moving in a horizontal plane ($x - y$), along the $x$-axis, at a certain height above the ground. It suddenly explodes into two fragments of masses $m/4$ and $3m/4$. An instant later, the smaller fragment is at $y = + 15$ cm. The larger fragment at the instant is at
A) $y = - 5$ cm
B) $y = + 20$m
C) $y = + 5$ cm
D) $y = - 20$ cm
Explanation
(a) Since there is no external force acting on the particle,
Hence
$y_{CM} = \frac{m_{1}y_{1} + m_{2}y_{2}}{m_{1} + m_{2}} = 0$, hence
$\left( \frac{m}{4} \right) \times ( + 15) + \left( \frac{3m}{4} \right)\left( y_{2} \right) = 0 \Rightarrow y_{2} = - 5$ cm
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.