Question

Two identical balls A and B each of mass "m" are moving towards each other at equal speed each of "v". Ball A initially is moving along the positive x direction while ball B is moving along negative x direction. If the collision is perfectly elastic, the impulse received by the ball B is

• A. $-mv$
• B. $-2mv$
• C. $mv$
• D. $2mv$

Answer 1

The correct option is D $2mv$

Since the collision is perfectly elastic, ball B travels in the backward direction i.e along positive x-axis with the same speed before collision.
The change in velocity becomes $v-(-v)=2v$
$\therefore$change in momentum$=m\left(2v\right)=2mv$.