Question

This is a modern physics question, so please no Newtonian mechanics :D

A lump of sticky goo, of mass 9m0 (<--M not) and moving at 0.80 c, collides with another lump of goo, of mass 12m0 (M not) and moving in the opposite direction at 0.60c. The lumps of goo stick together after collision.

How do I find the speed and mass of the resulting goo clump?

I have tried using conservation of energy but I cant help but think that somewhere in the answer a portion of the mass will transform into heat that is given off into the atmosphere.

Answer 1

When I use conservation of energy and assume that no energy is lost to heat I get that the velocity of the resulting lump is 0 and the mass is 30m (relative mass)

Answer 2

If I recall, momentum for a relativistic particle is \[p=\gamma m v\] instead of just \[p=mv\]which is the momentum of classical limit.