  Question

# A smooth sphere A of mass m collides elastically with an identical sphere B at rest. The velocity of A before collision is 8 m/s in a direction making 60∘ with the line joining the centres at the time of impact. Which of the following is/are possible:

A
the sphere A comes to rest after collision
B
the sphere B will move with a speed of  8  m/s  after collision
C
the direction of motion of A and B after collision are at right angles
D
the speed of B after collision is 4  m/s

Solution

## The correct options are C the direction of motion of A and B after collision are at right angles D the speed of B after collision is 4  m/s Sphere A moving with velocity v has a component v/2 along the line joining the centres of the spheres at the time of collision and another component v√3/2 perpendicular to the previous direction. After  collision the component along the line will interchange i.e B will move with v/2 velocity i,e  4 m/s along the line joining the centres and A moves with v√3/2 velocity at perpendcular direction to B.  Suggest corrections   