Q. 2 bodies of different masses of $2\ kg$ and $4\ kg$ are moving with velocities $20\ m/s$ and $10\ m/s$ towards each other due to mutual gravitational attraction. What is the velocity of their centre of mass
A) $5\ m/s$
B) $6\ m/s$
C) $8\ m/s$
D) Zero
Explanation
(d) $m_{1} = 2kg,\ m_{2} = 4kg,\ {\overrightarrow{v}}_{1} = 20m/s,{\overrightarrow{v}}_{2} = - 10m/s$
${\overrightarrow{v}}_{cm} = \frac{m_{1}{\overrightarrow{v}}_{1} + m_{2}{\overrightarrow{v}}_{2}}{m_{1} + m_{2}} = \frac{2 \times 20 - 4 \times 10}{2 + 4} = 0\ m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.