Energy of System: Which Statement is Always Correct?

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SUMMARY

The correct answer to the homework statement regarding the work done by various forces is E) None of the above. The discussion clarifies that the work of friction can be zero if there is no movement, the work of gravity is also zero for an object at rest, the work done by a spring varies depending on compression or elongation, and the normal force does no work when there is no movement. Each alternative statement is proven incorrect through specific examples.

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Fatima Hasan
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Homework Statement


Which of the following statements is always correct?

A) The work of friction force is negative.
B) The work of gravity is positive
C)The work of the spring is negative
D) The work of the normal force is negative
E) None of the above

The Attempt at a Solution


My answer is E

A) if applied force is smaller than to overcome the resistance then work of friction is 0 since no movement
B) a book on table has no movement so work of gravity = 0
C) spring can be compressed or elongated, either of which give opposite signs
D) book on table, work of normal force is 0 since no movementSo is my answer right!?
Thanks
 
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I agree with your answer and with the counter-examples you've given for the four alternatives.
 
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