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.

Answer 1

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.