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 97.0 kg. The mass of the rock is 0.350 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

Also, Find the speed of the wagon after the rock is thrown directly backward.

= ? m/s

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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