A ball of mass m approaches a wall of mass \[M\text{ }\left( >>m \right)\] with speed 4 m/s along the normal to the wall. The speed of wall is 1 m/s towards the ball. The speed of the ball after an elastic collision with the wall is -
A)5 m/s away from the wall
B) 9 m/s away from the wall
C) 3 m/s away from the wall
D) 6 m/s away from the wall
Correct Answer:
D
Solution :
Let v be the velocity of ball after collision, collision is elastic \[\therefore \,\,\,e=1\] or relative velocity of separation = relative velocity of approach \[\therefore \,\,\text{ }v-1=4+1\] or \[v\text{ }=\text{ }6\] m/s (away from the wall)