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Need Help on Gravitation Potential Energy Problem

[SOLVED] Need Help on Gravitation Potential Energy Problem

1. Homework Statement
(a) A 5.3 kg particle and a 3.0 kg particle have a gravitational attraction with a magnitude of 2.6 x10^-12 N. What is the gravitational potential energy of the two-particle system?


(b) If you triple the separation between the particles, how much work is done by the gravitational force between the particles?

(c) How much work is done by you?


2. Homework Equations
F=(GmM)/r^2
U=-(GmM)/r


3. The Attempt at a Solution

First I used the given information to solve for r using newtons law of gravitation. Then I pluged r=1.96E1 into the potential energy equation to get -5.41E-11J but that was wrong.
 

Answers and Replies

Hootenanny
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1. Homework Statement
(a) A 5.3 kg particle and a 3.0 kg particle have a gravitational attraction with a magnitude of 2.6 x10^-12 N. What is the gravitational potential energy of the two-particle system?


(b) If you triple the separation between the particles, how much work is done by the gravitational force between the particles?

(c) How much work is done by you?


2. Homework Equations
F=(GmM)/r^2
U=-(GmM)/r


3. The Attempt at a Solution

First I used the given information to solve for r using newtons law of gravitation. Then I pluged r=1.96E1 into the potential energy equation to get -5.41E-11J but that was wrong.
Recheck your arithmetic, you separation value is incorrect.
 
is R=2.012E1 and U=-5.25E-11 correct
 
Hootenanny
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Also would the solution to part b be U=-(GMm)/3r
 
Hootenanny
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Also would the solution to part b be U=-(GMm)/3r
Not quite, the work done is change in gravitational potential energy.
 
Work=((-GMm)/3r)-((-GMm)/r)
 
Hootenanny
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I got 3.5E-11J but that was also incorrect
 
Hootenanny
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I got 3.5E-11J but that was also incorrect
I get something different. Furthermore, be careful with the sign.
 
I got ((-GMm)/3r)=-1.75E-11J and ((-GMm)/r)=-5.25E-11J
is((-GMm)/3r)=-1.75E-11J correct?
 
Hootenanny
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I got ((-GMm)/3r)=-1.75E-11J and ((-GMm)/r)=-5.25E-11J
is((-GMm)/3r)=-1.75E-11J correct?
Yes, your calculations are correct, just be aware of the sign of your final answer.
 
work=-3.50E-11J
 
because work is equal to the negative change in potential energy
 
and part c is 3.50E-11J
 
Hootenanny
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thank you for your help
 
Hootenanny
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