Question
A child is pulling two red wagons, with the second one tied to the first by a (non-stretching) rope. Each wagon has a mass of 10 kg. If the child exerts a force of 30 N for 5.0 m, how much has the kinetic energy of the two-wagon system changed?
- 300 J
- 150 J
- 75 J
- 60 J
Final Answer
(b)
Solution video
OpenStax College Physics for AP® Courses, Chapter 7, Problem 16 (Test Prep for AP® Courses)
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Video Transcript
This is College Physics Answers with Shaun Dychko. Two wagons are tied to each other and then a child is exerting a force of 30 newtons on one of them. We assume that the system is frictionless, that it starts at rest although it doesn't matter if it starts at rest or not but it certainly matters that it's frictionless and that the child is pulling horizontally and the system is moving horizontally in which case the change in kinetic energy is the net work done— that's the work-energy theorem— and the net work is the net force multiplied by the distance over which the force is applied and the net force is 30 newtons multiplied by 5.0 meters, which is 150 joules is the change in kinetic energy. So the answer is (b).