A ball collides elastically with another ball of the same mass. The collision is oblique and initially oneoftheballs was at rest. Afterthe collision,the two balls move with same speed. What will be the angle between the velocitiesof the balls after the collision? 

a) 

b) 

c) 

d) 

A ball collides elastically with another ball of the same mass. The collision is oblique and initially oneoftheballs was at rest. Afterthe collision,the two balls move with same speed. What will be the angle between the velocitiesof the balls after the collision? 

a) 

b) 

c) 

d) 

(d)
Applying law of conservation of momentum, we get
(i)
(ii)
According to law of conservation of KE,
or (iii)
From Eqs.(ii) and (iii),we have
Or or