physics
posted by Sarah .
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 96.5 kg. The mass of the rock is 0.250 kg. Initially the wagon is rolling forward at a speed of 0.460 m/s. Then the person throws the rock with a speed of 16.5 m/s. Both speeds are relative to the ground. Find the speed of the wagon after the rock is thrown directly forward.
m/s
Find the speed of the wagon after the rock is thrown directly backward.
Do I use conservation of energy equation?

No, use conservation of momentum
initial momentum= final momentum
96.5*.460=(96.5.250)Vwagon+.250(16.5) 
Thanks. Got it