Awagon 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.