- #1
mike-d
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Homework Statement
How much work must you perform to lift a 5 kg bag from the floor to the countertop, 1 meter above the floor?
2. The attempt at a solution
A. You could say that any force greater than the weight of the bag would lift it up. Thus, the weight is 50 N and the force should at least 50 N and above.
since W= F * d * cos(theta)
W = 50 * 1 * cos0 = 50 Joules
B. My classmates insist that this is the correct way. The net work is equal to the change in potential energy, and the total work includes: Work done by weight, and work done by the force...
Work of weight = 50 * 1 * cos180 = -50 Joules
deltaPotential energy = PE2 -PE1 = 50 - 0 = 50 Joules
W(total) = W(weight) + W(force) = deltaPE
-50 + W(force) = 50 joules ==> W(force) = 100 Joules
Can anyone tell me which answer is the correct one? It seems to me that the second answer would be correct if you pulled the bag up suddenly and let it go and it would then stop mid-air at 1 meter. Can anyone verify this? Thanks in advance :)