An 8.0 kg puck floating on an air table is travelling east at 15 cm/s. Coming the other way at 25 cm/s is a 2.0 kg puck on which is affixed a wad of bubble gum. The two slam head-on into each other and stick together. Find their velocity after the impact. How much kinetic energy was lost?

Answer 1

m1v1+m2v2 = v'(m1+m2)
This is the equation you must use so...

(8*15)+(2*(-25)) = v'(8+2)
The velocity for 25cm/s is negative because it's approaching the first puck in the opposite direction. Just find v' to find the velocity after impact.

Not sure for lost KE. Sorry.