Two skaters collide and grab on to each other on frictionless ice.?

Question

One of them, of mass 70.0 kg, is moving to the right at 2.00 m/s, while the other, of mass 75.0 kg, is moving to the left at 2.80 m/s.
What are the magnitude of the velocity of these skaters just after they collide?

Answer 1

This is an inelastic collision. Momemtum is conserved.

Initial momentum = ( 70.0 kg ) ( + 2.00 m/s ) + ( 75.0 kg ) ( -2.80 m/s)

Final momentum = ( 70.0 kg + 75.0 kg ) ( v )

Set these two expressions equal and solve for v. If it's positive, it's towards the right; negative is towards the left.