The work-energy theorem says that the work done on an object equals the change o
ID: 1433477 • Letter: T
Question
The work-energy theorem says that the work done on an object equals the change of kinetic energy of an object. At the gym, you lift a heavy dumbbell over your head. When your arms are fully extended, the dumbbell is once again at rest. Did you do work on the dumbbell?
No work was done by you on the dumbbell since it is has not changed its kinetic energy
Yes, the dumbbell is hotter than it was below
Yes, but gravity did the same amount of negative work
1.No work was done by you on the dumbbell since it is has not changed its kinetic energy
2.Yes, the dumbbell is hotter than it was below
3.Yes, but gravity did the same amount of negative work
Explanation / Answer
Yes, but gravity did the same amount of negative work
The work-energy theorem is accurate as stated: the work done by the net force leads to a change in kinetic energy. If you want to consider the work done by by forces other than gravity, then you can say that that work done equals the change in KE + PE
Say you lift an object of mass m a height h at constant speed. The force you apply (up) must equal the weight (down), so the net force is zero. Thus, according to the W-E theorem, the change in KE is zero. On the other hand, if you only consider the applied force F=mg (up), then the work done by that force is mgh, which equals the change in "KE + PE" which is mgh.
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