What's the velocity of the ball bearing

Question

A ping pong ball (0.15kg) strikes a stationary ball bearing (2kg) head on at 15m/s forward. The ping pong ball ricochete's backwards 12m/s after the strike what is the resulting velocity of the ball bearing

Answer 1

Linear momentum is conserved.  Assume right is positive direction and ping pong ball initially is moving right.

 

m = ping pong ball mass = 0.15 kg

v₁ = initial velocity of ping pong ball = 15 m/s

v₂ = final velocity of ping pong ball = -12 m/s

 

M = mass of ball bearing = 2 kg

u₁ = initial velocity of ball bearing = 0

u₂ = final velocity of ball bearing = ?

 

mv₁ + M(0) = mv₂ + Mu₂

 

u₂ = (mv₁ - mv₂) / M = (m/M)(v₁ - v₂) = (0.15/2)[15 - (-12)] m/s = 2.025 m/s