Expression for the gravitational potential Vgrav

[c_m]

Homework Statement

In a system where other gravitational influences can be discounted, two particles of equall mass m, are fixed at positions x= 0 and x= x0 on the x-axis.

1) derive an expression for the gravitational potential Vgrav at a general position x on the x-axis.?

Homework Equations

The only equations i can seem to find are:

A) for a test mass m at a distance r from another mass M
Vgrav(r) = (1/m)Egrav = (1/m)(-GmM/r) = -GM/r

B) V(r) = Q/ 4pie e0 r
Where e0 is the permittivity of free space

The Attempt at a Solution

Well to derive an expression usually means i have to combine and rearrange two separate expressions, but i do not know where to begin, maybe i don't need either of these expressions? could somebody please help me to understand what is goin on here? and prehaps where to start looking?

 

[Kurdt]

Equation A you have there is the gravitational potential. Equation B is the electrostatic potential so you won't need that. So you have two masses along the x-axis and you want to know the potential along the axis dues to those two masses. How do you think you should proceed from here?

 

[c_m]

Thankyou for relpying

I have actually sent my work now but i did not really do this one, so i would still like to go through it to see what i should have done.

So i do need equation A then? but not B. do i need to find another expression now then for the potential? I just didnt know where to begin.

 

[Kurdt]

When there is more than one mass involved you can sum the potentials.

 

[c_m]

you mean like, V = G m1 m2 / r? rather than V = Gm/r?

 

[Kurdt]

No. Work out the potential using equation A due to one mass, then the other and then add them together to find the potential due to both.