Question

A body of mass m moving with velocity v suffers head on elastic collision with another body of mass 2m at rest. The ratio of the kinetic energy of the colliding body before and after collision is:

• A. 9:1
• B. 12:1
• C. 16:1
• D. 18:1

Answer 1

Answer: (A)

9:1

There is no external force hence momentum of the system will be conserved.
$[m\times u_1=m\times v_1+2\times m\times v_2]$
equation of coefficient of restitution will be
$v_2-v_1=u_1$
on solving it gives,
$[v_1=(-u_1\left)/3\right]$
KE is directly proportional to $\left[v^2\right]$
therefore ratio of the final is to initial kinetic energy will be
$9/1$