A 0.115-kg hockey puck, moving at 35.0 m/s, strikes a 0.265-kg octopus thrown onto the ice by a hockey fan. The puck and octopus slide off together. What is their velocity?
[No octopus was armed in the solution of this question!]
This should be an inelastic collision where the two bodies, after impact, stick together forming one object having the mass composed by the sum of the individual ones.
I assume that the octopus, at the moment of impact, is at rest.
Using our data we get: