# Homework Help: Change in the Earth's orbit radius from changing mass of the Sun

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1. May 26, 2017

### Rwindsor1

1. The problem statement, all variables and given/known data
Consider the earth's orbit around the sun orbit as circular. Suppose the sun slowly loses mass from mass M1 to mass M2. Suppose that the initial orbit is R1 and the final orbit is R2. Express R2 in terms of the other parameters.
2. The attempt at a solution
The problem I'm having here is relating the two equations for the gravitational force initially and finally. I can't think what is conserved in this situation. The final answer is supposed to be M1R1/M2. Looks like something to do with moments but I can't figure out what.

Last edited: May 26, 2017
2. May 26, 2017

### jbriggs444

Are there any unbalanced external torques?
You seem to have mis-quoted the answer.

3. May 26, 2017

### Rwindsor1

Apologies, corrected now. And I don't believe there is, but when I tried moments I was always left with one too many variables to solve the equation

4. May 26, 2017

### jbriggs444

If you have too many variables then likely you need more equations. But you have not shown any equations. There was a place on the homework template for them.

5. May 26, 2017

### Rwindsor1

This is what I meant by I feel there is something else that must be conserved. I know I need another equation, I just don't know what that is.

6. May 26, 2017

### jbriggs444

Something else? What thing have you decided is conserved so far?