How is Gravitational Potential Calculated on the Moon's Surface?

[Pho3nix]

[SOLVED] Gravitation Problem

Homework Statement

The moon has a mass of 7.7times10^22kg and radius 1.7times10^6m. Calculate:
a) The gravitational potential at its surface.
b) The work needed to completely remove a 1.5times10^3kg spacecraft from its surface into outer space.
c) What is the minimum speed which a body must have to escape from the moons gravitational field?

Homework Equations

Vg=-GM/r
Ep=GMm/r
Ek=.5m(vsquared)
Vg is the gravitational potential
Ep is potential energy

The Attempt at a Solution

a) Vg=GM/r
G=6.67times10^-11
M=7.7times10^22kg
r=1.7times10^6m
Plug in the numbers and I get -3.0times10^6
b)Ep=Gmm/r
M=7.7times10^22Kg
m=1.5times10^3Kg
r=1.7times10^6
Plug in numbers and get -4.5times10^9 Joules
c)In need help on this one.

 

[Shooting Star]

c)In need help on this one.

Equate the KE to the work done in (b). That gives you the minimum v, which is called the escape velocity, which is the minimum speed that has to be given to the body remove it to infinite distance.