# Homework Help: Gravity and height

1. Jan 28, 2007

### NIZBIT

I have a problem like the one below:

I understand how they derived it(I did the same thing) but never say what is the height. So could someone tell what the height is?

2. Jan 28, 2007

### Chi Meson

In that problem, height is relative to the radius of the planet. The correct answer for THAT question should have been
$$r = \sqrt{2}*R$$.
That would be the orbital radius. The "height" would be the altitude above the planet, which would be
$$(\sqrt{2}*R)-R$$
or$$(\sqrt{2}-1)*R$$
Which happens to be equal to 0.41*R

Substitute the radius of the planet in for R and you get the "height."

3. Jan 29, 2007

### NIZBIT

Ok I see now. Wasn't so obvious last night.