Gravitational potential energy of the moon

[UrbanXrisis]

How much work is done by the moon's gravitational field as a 1000kg meteor comes from outer space and impacts the moon's surface?

all I have to do is:
$$U=-\frac{Gm_1m_2}{r}$$
where $$_{m_1}$$ is the mass of the moon, $$_{m_2}$$ is the mass of the meteor, and $$_{r}$$ is the radius of the moon. is that correct?

 

[whozum]

Well you want to integrate the gravitational force from infinity to the Earth's surface, because what 'r' ar eyou going to be using there?

 

[vincentchan]

Well you want to integrate the gravitational force from infinity to the Earth's surface, because what 'r' ar eyou going to be using there?

well, after the integration, you will get his equation:
$$U=-\frac{Gm_1m_2}{r}$$
whereas the r is the redius of the moon as UrbanXrisis suggest...

 

[whozum]

Oh, I didnt see he specified r.