Q. A body of mass $m_{1}$ moving with uniform velocity of $40\ m/s$ collides with another mass $m_{2}$ at rest and then the two together begin to move with uniform velocity of $30\ m/s$. The ratio of their masses $\frac{m_{1}}{m_{2}}$ is
A) 0.75
B) 1.33
C) 3.0
D) 4.0
Explanation
(c) Initial momentum of the system $= m_{1} \times 40 + m_{2} \times 0$
Final momentum of the system $= (m_{1} + m_{2}) \times 30$
By the law of conservation of momentum
$m_{1} \times 40 + m_{2} \times 0 = (m_{1} + m_{2}) \times 30$
$\Rightarrow 40m_{1} = 30m_{1} + 30m_{2} \Rightarrow 10m_{1} = 30m_{2} = \frac{m_{1}}{m_{2}} = 3$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.