Question

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 this instant is at

• A. $y=-5\,cm$
• B. $y=20\,cm$
• C. $y=+5\,cm$
• D. $y= - 20\,cm$

Answer 1

Answer: (A)

$y=-5\,cm$

Answer 2

Since there is no external force acting on the particle, hence $y_{CM}=\frac{m_{1}y_{1}+m_{2}y_{2}}{m_{1}+m_{2}}=0$, $\therefore \left(\frac{m}{4}\right)\times\left(+15\right)+\left(\frac{3m}{4}\right)\left(y_{2}\right)=0$ $\Rightarrow y_{2}=-5\, cm$