# A ball of mass  moving with velocity  makes an oblique elastic collision with a stationary ball of mass 2  The angle of divergence between the balls after  collision in ground frame, if the ball of mass  turns by an angle of  in centre of mass frame is a) b) c) d)

## Question ID - 100211 | SaraNextGen Answer A ball of mass  moving with velocity  makes an oblique elastic collision with a stationary ball of mass 2  The angle of divergence between the balls after  collision in ground frame, if the ball of mass  turns by an angle of  in centre of mass frame is a) b) c) d)

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(d)

Let us solve this question in  frame. As the collision is elastic, the magnitude of momenta of all balls remains same after collision in this frame

Velocity of  frame w.r.t. ground frame is

The momentum diagram in  frame is drawn as shown in fig.

Now, velocity of  after colision in  frame is while that of  is  along   and ,  respectively. Let  and  be the velocities of  and , respectively after collision in ground frame, then velocity vector diagrams can be drawn as shown

Using trigonometry, from upper triangle

From lower triangle:

So, angle of divergence is

Alternative method  Write down conservation of momentum equations, coefficient of restitution equation, energy conservation and use the given conditions