What is the Work Done by Gravity on an Object Moved Straight Up?

AI Thread Summary
The work done by gravity on an object moved straight up is calculated as -mgh, indicating that gravity does negative work when lifting the object. As the object gains potential energy (+mgh), the force of gravity acts in the opposite direction to the displacement. This relationship is confirmed by Newton's third law, which states that the work done by gravity is negative when the object is lifted. Understanding the direction of both the displacement and gravitational force is crucial in determining the correct answer. Therefore, the correct choice is (c) -mgh.
NathanLeduc1
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Homework Statement


An object of mass m is moved straight up by a distance h. The work that gravity does on the object is:
(a) -mh
(b) +mh
(c) -mgh
(d) +mgh
(e) None of the Above

Homework Equations


Work = ∫F dl
PE = mgh

The Attempt at a Solution


I have a feeling the answer is (c) -mgh because work is done to lift the object. The object is gaining potential energy so it's gaining +mgh and due to Newton's 3rd law, the work done by gravity is -mgh. Is that right?
 
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NathanLeduc1 said:

Homework Statement


An object of mass m is moved straight up by a distance h. The work that gravity does on the object is:
(a) -mh
(b) +mh
(c) -mgh
(d) +mgh
(e) None of the Above

Homework Equations


Work = ∫F dl
PE = mgh

The Attempt at a Solution


I have a feeling the answer is (c) -mgh because work is done to lift the object. The object is gaining potential energy so it's gaining +mgh and due to Newton's 3rd law, the work done by gravity is -mgh. Is that right?

Yes, it's answer (c) . But you can get it directly from the definition of work.

What is the direction of the displacement?

What is the direction of the gravitational force?
 
Ah, right, hadn't thought of that. The direction of the displacement is opposite the direction of the force. Thank you.
 

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