A 70.0 kg ice hockey goalie at rest catches a 0.150 kg puck moving at 35.0 m/s, and they move off together. What is their common final velocity?

1. Because the goalie catches the puck, this is a perfectly inelastic collision and the two share a final velocity. 2. Momentum conservation gives (0.150 kg)(35.0 m/s) equal to (0.150 kg + 70.0 kg) times the final velocity. 3. The left side gives 5.25 kg m/s, and the combined mass is 70.15 kg. 4. Dividing gives a final velocity of about 0.0748 m/s. 5. 7.48 m/s and 0.748 m/s are each off from the correct value by a factor of a hundred or ten, and 35.0 m/s ignores that the goalie's large mass must also be accelerated. _Source: OpenStax College Physics (CC BY 4.0), Ch 8 "Linear Momentum and Collisions", section 8.5 Inelastic Collisions in One Dimension_