Are their any Physics tutors on here tonight?!
posted by Megan .
A cart of mass M1 = 6.00 kg and initial speed = 4.00 m/s collides head on with a second cart of mass M2 = 4.00 kg at rest. Assuming that the collision is elastic, find the speed of M2 after the collision.

write the conservatoin of momentum equation, you get two unknowns, which are the final speeds of each cart.
solve this equation for one of the speeds in terms of the other.
Then, write the conservation of energy equation. PUT the value of the expression you just found above in for one of the speeds, you then have an equation with one unknown.
Have fun, a lot of algebra.