Need Help on Gravitation Potential Energy Problem

[SOLVED] Need Help on Gravitation Potential Energy Problem

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?

F=(GmM)/r^2
U=-(GmM)/r

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.

Hootenanny
Staff Emeritus
Gold Member

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?

F=(GmM)/r^2
U=-(GmM)/r

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
Staff Emeritus
Gold Member
is R=2.012E1 and U=-5.25E-11 correct
Correct indeed Also would the solution to part b be U=-(GMm)/3r

Hootenanny
Staff Emeritus
Gold Member
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
Staff Emeritus
Gold Member
Work=((-GMm)/3r)-((-GMm)/r)
Much better I got 3.5E-11J but that was also incorrect

Hootenanny
Staff Emeritus
Gold Member
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
Staff Emeritus
Gold Member
I got ((-GMm)/3r)=-1.75E-11J and ((-GMm)/r)=-5.25E-11J
is((-GMm)/3r)=-1.75E-11J correct?

work=-3.50E-11J

because work is equal to the negative change in potential energy

and part c is 3.50E-11J

Hootenanny
Staff Emeritus