Which forces are doing work?
Classical Mechanics
Level
2
As you push the box of potatoes across the level ground to your Uncle Bob's house at about a constant speed, which forces are doing work?
The force you are applying and friction
The force you are applying, friction, and gravity
The force you are applying, friction, gravity, and the supporting force from the ground.
Only the force you are applying.
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1 solution
The only forces with a vector component parallel to the displacement vector of the box of potatoes are the applied force and friction. Both the weight of the box of potatoes (the force due to gravity) and the force of the ground on the box of potatoes are normal to the displacement - so the work done to the box by those forces is zero.