# Help me!

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• Jul 12th 2006, 11:18 AM
pocahontas
Help me!
The gravitational potential energy of a 2.0 kg object, near the surface of the Earth, has decreased by 10J. Which of the following can you determine with this information? Please explain your answer.
a. the initial height of the object.
b. the final height of the object.
c. both the initial and final height of the object.
d. the difference between the initial and final height
Can you explain what has physically happened to the object in this scenario?
• Jul 12th 2006, 02:24 PM
topsquark
Quote:

Originally Posted by pocahontas
The gravitational potential energy of a 2.0 kg object, near the surface of the Earth, has decreased by 10J. Which of the following can you determine with this information? Please explain your answer.
a. the initial height of the object.
b. the final height of the object.
c. both the initial and final height of the object.
d. the difference between the initial and final height
Can you explain what has physically happened to the object in this scenario?

We only know $\Delta GPE$ so all we can say is the difference in height. Recall that the zero for GPE is at an arbitrary height. So the answer is d).

Since the GPE has been reduced, or $\Delta GPE < 0 \, J$, we know that $mgh - mgh_0 < 0$ or $h. Therefore the height of the object has been reduced, or in plainer language, the object has dropped $\frac{10 \, J}{mg}$ = 0.51 m.

-Dan