Quick questions on work and energy

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  • #1
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Can work be done on a system if there is no motion?
I would say no, no motion = no energy...

Is it possible for a system to have negative potential energy?
I would say yes, since the choice of the zero of potential energy is arbitrary.

A 500-kg elevator is pulled upward with a constant force of 550N for a distance of 50 m. What is the work done by the 550N force?
From what I understand, we multiply 550N by 50 m, and get about 3.00x 104 J.

Thanks for your help!
 

Answers and Replies

  • #2
Dick
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I think you are pretty much correct.
 
  • #3
berkeman
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I would agree with you on all three. But the first question is thought provoking. I wonder if we can think of a case where there is work done, but no motion. Certainly that is true in cases where there is no *net* motion, like spinning a wheel with friction bearings. But no motion at all....hmmm.

Chemical energy conversion...is that considered work? I don't think so, but maybe someone else can think of a creative case.
 
  • #5
AlephZero
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Can work be done on a system if there is no motion?
I would say no, no motion = no energy...

You can't do mechanical work without motion, but there are other ways to increase the energy of a system - for example adding heat energy, or storing electrical charge in a capacitor. "Increasing the energy" is the same as "doing work".

Is it possible for a system to have negative potential energy?
I would say yes, since the choice of the zero of potential energy is arbitrary.

A 500-kg elevator is pulled upward with a constant force of 550N for a distance of 50 m. What is the work done by the 550N force?
From what I understand, we multiply 550N by 50 m, and get about 3.00x 104 J.

Both correct.
 

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