A wagon is rolling forward on level ground. Friction is negligible. The person s

Question

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 93.0 kg. The mass of the rock is 0.260 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 16.5 m/s. Both speeds are relative to the ground. Find the speed of the wagon after the rock is thrown directly forward. Then, find the speed of the wagon after the rock is thrown directly backward.

Explanation / Answer

Applying conservation of momentum .. (forward positive)

For rock thrown forwards ..
Wagon mom. before = wagon mom. after (vel=v) + rock mom.
93.0kg x 0.52m/s = (93.0kg x v) + (0.26kg x 16.50m/s)

44.07 = 93.0v .. .. ..

v = 0.47387 m/s .. (0.474)

For rock thrown backwards .. (- mom.)
Wagon mom. before = wagon mom. after (vel=v) - rock mom.
93.0 x 0.52 = (93.0 x v) - (0.26 x 16.50)

52.65 = 93.0v .. .. ..

v =0.56612 m/s .. (0.566)

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