In that same goalie and puck collision, how much kinetic energy is lost from the puck's original 91.9 J of kinetic energy?

1. Before the collision, only the puck moves, so the internal kinetic energy is one half times 0.150 kg times (35.0 m/s) squared, which is about 91.9 J. 2. After the collision, the combined 70.15 kg mass moves at about 0.0748 m/s, giving a kinetic energy of about 0.196 J. 3. The change in internal kinetic energy is 0.196 J minus 91.9 J, which is about negative 91.7 J. 4. That means about 91.7 J was lost, almost all of the puck's original kinetic energy, converted mostly to heat and sound. 5. 0.196 J is the small amount of kinetic energy left afterward, not the amount lost, so it should not be confused with the answer to this question. _Source: OpenStax College Physics (CC BY 4.0), Ch 8 "Linear Momentum and Collisions", section 8.5 Inelastic Collisions in One Dimension_