Quick questions about Gravity in unit 3/4

[something5678]

Hi Guys,

could someone please help me with this problem?

There is a point between the earth and moon where the two gravitational fields cancel each other out. Determine this distance from earth if the moon is 3.84X10^8m away.

Also, the question doesn't give the mass of the earth or the mass of the moon, am I suppose to use them anyway?

Thanks!! 

[PB]

Hmm, first of all, the mass of Earth is given in the Physics formula sheet (ME = 5.98 × 10^24 kg). However, I think you would also need the mass of the moon (which is not provided in the formula sheet).  If anything, they should have given it to you in the question.
So what are you supposed to do?
Well the question states that there is point btwn Earth and Moon where the two grav fields cancel out and they want you to find out how far from Earth this point is.
Theoretically, an object can be stationary at that point without being dragged in by either of the two bodies' gravity wells.
So we know that this point is 3.84x10^8m away from the moon right? So lets calculate the grav field at that point produced by the moon, and that would mean that the earth would have to be exerting the same grav field at this point too (because the cancel out)!

Using the formula, g = (G • Mmoon)/r2, you can find g.   Then, use that g to equate to (G • Mearth)/R2, thus finding R. Wah lah!

[PB]

*Mmoon = find out on the internet
r = 3.84x10^8m

I hope that makes sense, and more importantly, I hope that is correct :PPP I have not got any of my formulas/notes with me and I am a bit rusty lols