Question

A big ball of mass $M$, moving with velocity $u$ strikes a small ball of mass $m$, which is at rest. Finally small ball obtains velocity $u$ and big ball $v$. Then what is the value of $v$ ?

• A. $ \frac{M-m}{M}u $
• B. $ \frac{m}{M+m}u $
• C. $ \frac{2m}{M+m}u $
• D. $ \frac{M}{M+m}u $

Answer 1

Answer: (A)

From law of conservation of momentum
$ {{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}={{m}_{1}}{{v}_{1}}+{{m}_{2}}{{v}_{2}} $
$ \Rightarrow $ $ Mu+m\times 0=Mv+Mu $
$ \Rightarrow $ $ v=\frac{M-m}{M}u $