A smooth sphere A of mass $m$ collides elastically with an identical sphere b at rest. The velocity of A before collision is $10m/s$ in a direction making ${60}^0$ with the line of centres at the time of impact.

 

In elastic collision of identical bodies velocity interchanged in common normal directional and  velocity of the bodies remains unchanged along common tangent directions.

Component of velocity of A along common normal is $v\cos {60}^0$ and this velocity of A after collision with B is interchanged. Hence A moves along $v\sin {60}^0$ which is normal to common normal