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Classical Mechanics
Level
3
When the box of potatoes falls through the air over the 10-meter cliff, it starts very slowly but gains speed. If the 50-pound box of potatoes is going 10 meters per second right before it hits the ground, how much work did air resistance do?
1,070 Joules
0 Joules
1,150 Joules
2,220 Joules
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1 solution
The box of potatoes gains kinetic energy as it falls because gravity is doing more work than air resistance is. The total work done by gravity is equal to the weight of the potatoes times the vertical height of the cliff. If there were no air resistance, this work would be equal to the kinetic energy at the bottom. The work done by gravity less the work done by the force of air resistance is equal to the kinetic energy right before it hits the ground.