Question

Three identical spherical balls $A, B\, and \,C$ are placed on a table as shown in the figure along a straight line. $B$ and $C$ are at rest initially.
The ball $A$ hits $B$ head on with a speed of $ 10\,ms^{-1}$ . Then after all collisions (assumed to be elastic) $A$ and $B$ are brought to rest and $C$ takes off with a velocity of

• A. $ 5\,ms^{-1}$
• B. $ 10\,ms^{-1}$
• C. $ 2.5\,ms^{-1}$
• D. $ 7.5\,ms^{-1}$

Answer 1

Answer: (B)

Here, $u_{1}=10,\, m_{1}=m,\, m_{2}=m,\, u_{2}=0$
$u_{1}=10\, m / s$
$v_{2}=\left[\frac{m_{2}-m_{1}}{m_{1}+m_{2}}\right]$
$u_{2}+\frac{2 m_{1} u_{1}}{m_{1}+m_{2}}$
$=\frac{2 \times m \times 10}{2 m}=10\, m / s$
Similarly, for $B$ and $C$
$\Rightarrow v_{3}=10\, m / s$