physics
posted by Sam .
A wagon is rolling forward on level ground. Friction is negligible. The person sitting in the wagon is holding a rock. The total mass of the wagon, rider, and rock is 94.0 kg. The mass of the rock is 0.350 kg. Initially the wagon is rolling forward at a speed of 0.520 m/s. Then the person throws the rock with a speed of 17.5 m/s. Both speeds are relative to the ground. Find the speed of the wagon after the rock is thrown directly forward.

Total momentum is constant.
Write that as an equation and solve for trhe new wagon speed, V'.
94*0.52 = 93.65 V' + 0.345*17.5
If the rock had been trown backwards, there would be a minus sign before the last term.