Question

A ball of mass $m$ elastically collides with a wall with velocity $v$, the $n$ change in its momentum is equal to

• A. 2 m
• B. 2 mv
• C. 8 mv
• D. zero

Answer 1

Answer: (B)

2 mv

Answer 2

If after the collision of two bodies, the total kinetic energy of the bodies remains the same as it was before collision and momentum remains conserved, then collision is perfectly elastic. Let the direction in which ball is moving be taken as positive, after collision with the wall the direction of velocity is reversed. Hence, change in momentum is initial momentum - final momentum $=m v-(-m v)=2 m v$