Up the hill!
Now your resolve will truly be tested. Your Uncle Bob lives on a hill. The nice level ground is now replaced by a ridiculously steep hill. You now need to push the box of potatoes with a force of 40 pounds (178 Newtons) in order to continue to keep it going at about a constant speed. You will get these potatoes to Bob if it kills you. What forces are doing work?
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1 solution
There is now a component of the gravitational force in the opposite direction of the motion, so the force due to gravity is doing work to the box of potatoes in addition to the applied force and friction. The supporting force is not doing work. The supporting force is always perpendicular to the support - this is why it is sometimes called the "normal force". Since the displacement of the box of potatoes is still parallel to the ground, there is no component of the supporting force that is parallel to the displacement vector.