Question

Ball A moving with certain velocity strikes another ball B which is at rest. Ball B is three times heavier than ball A. After collision, ball B starts moving in forward direction with half the velocity of the initial velocity of ball A. Ball A, after collision, will move with the same velocity :

• A. As that of ball B, but in forward direction
• B. As before, but in backward direction
• C. As before, but in forward direction
• D. As that of ball B, but in backward direction

Answer 1

The correct option is D As that of ball B, but in backward direction

According to conservation of momentum

$m\times u+3m\times 0=m\times v+3m\times \frac{u}{2}$

$⟹mv=mu-\frac{3mu}{2}$

$⟹mv=\frac{-mu}{2}$

$⟹v=\frac{-u}{2}$

So, the ball A moves with same velocity as of ball B but in opposite direction.