A railroad diesel engine weighs four times as much as a freight car. The diesel engine coasts at 4.8 km/h into a freight car that is initially at rest. Part A Use conservation of momentum to find a speed at what the engine + car coast after they couple together. Express your answer to two significant figures and include the appropriate units.

Question

Physics

Ingrid Gibson

26 April, 19:22

A railroad diesel engine weighs four times as much as a freight car. The diesel engine coasts at 4.8 km/h into a freight car that is initially at rest. Part A Use conservation of momentum to find a speed at what the engine + car coast after they couple together. Express your answer to two significant figures and include the appropriate units.

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Answers (1)

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Nehemiah Wade · Answer 1

3.8 km/h

Explanation:

Conservation of momentum means that momentum stays the same when two objects collide. In this case, we can say that the freight car has mass x kg, and the engine has a mass of 4x kg. Since momentum is speed times mass, we have the initial momentum at 4.8km/h * 4xkg, or 19.2xkg*km/h. After they collide, the mass changes to 5x kg. this means that because the momentum stays the same, the speed will change. Since, again, momentum is speed times mass, we can say that the new speed is 19.2xkg*km/h / 5x*kg, or 3.84 km/h. Since this is to 2 significant figures, this is 3.8 km/h.