Q. Two solid rubber balls $A$ and $B$ having masses 200 and $400\ g$ respectively are moving in opposite directions with velocity of $A$ equal to $0.3\ m/s$. After collision the two balls come to rest, then the velocity of $B$ is
A) $0.15\ m/sec$
B) $1.5\ m/sec$
C) $- 0.15\ m/sec$
D) None of the above
Explanation
(c) Initial linear momentum of system $= m_{A}{\overrightarrow{v}}_{A} + m_{B}{\overrightarrow{v}}_{B}$
$= 0.2 \times 0.3 + 0.4 \times v_{B}$
Finally both balls come to rest
$\therefore$ final linear momentum $= 0$
By the law of conservation of linear momentum
$0.2 \times 0.3 + 0.4 \times v_{B} = 0$
$\therefore v_{B} = - \frac{0.2 \times 0.3}{0.4} = - 0.15\ m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.