Help with Escape Velocity Problem

[CaptainEvil]

I know that escape velocity is given by v^2 = 2GM/r

My question is what is the approximate escape speed needed to completely escape the moon & Earth's gravity.

Is it the sum of their individual Escape velocities? or is it one equation, with the radius' added and masses added?

Thanks

 

[mgb_phys]

I would add the escape velocities, the value for the moon is pretty small anyway

 

[CaptainEvil]

Yea I was thinking that something (i.e moons EV) would be negligable since the question asked for the approximate value. But are you sure of that? Wouldn't it make sense astronomically - for something to escape moon's and Earth's gravity - that's on the moon, to have to travel slightly slower than Earth's EV since now we are much farther away?

 

[mgb_phys]

I read it to mean at a great distance from both what's the escape velocity, ie. of the earth-moon system, in which case the Earth and moon's masses add so you can approx add their escape Vs

 

[CaptainEvil]

The exact wording of my problem is as follows:

"assuming one wished to escape completely from both the moon and Earth's gravity, what would the approximate escape speed be from the moon?"

 

[mgb_phys]

Thats why I would regard it as a single object - and so for a first approximation add the escape Vs