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

In summary, the work done by gravity on an object of mass m moved straight up by a distance h is -mgh. This is because the object gains potential energy, represented by +mgh, while the work done by gravity is in the opposite direction, represented by -mgh. This can also be derived from the definition of work, where the direction of the displacement is opposite the direction of the force.
  • #1
NathanLeduc1
37
0

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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  • #2
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?
 
  • #3
Ah, right, hadn't thought of that. The direction of the displacement is opposite the direction of the force. Thank you.
 

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

What is work done by gravity?

The work done by gravity is the amount of energy that is expended when an object is moved against the force of gravity. It is a measure of the force and distance involved in lifting or moving an object against the pull of gravity.

How is work done by gravity calculated?

The work done by gravity can be calculated by multiplying the force of gravity (usually 9.8 m/s^2) by the height or distance that the object is lifted or moved against gravity. This can be represented by the equation W = mgh, where W is the work done, m is the mass of the object, g is the acceleration due to gravity, and h is the height or distance moved.

What units is work done by gravity measured in?

The units for work done by gravity are joules (J), which is a unit of energy. This is because work is a measure of energy and is defined as the force applied over a distance.

Can work done by gravity be negative?

Yes, work done by gravity can be negative if the object is moving in the opposite direction of the force of gravity. This can happen when an object is being lowered or moved downward against gravity, resulting in a negative work value.

How does the angle of the incline affect work done by gravity?

The angle of the incline can affect the amount of work done by gravity. If the object is moved along an incline, the force of gravity is acting at an angle, which means that only a component of the force is acting in the direction of motion. This will result in less work being done compared to lifting or moving the object vertically.

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