# Homework Help: Physics Gravitational Force Question

1. Jan 3, 2006

### neoking77

At a distance H above the surface of a plane, the true weight of a remote probe is one percent less than its true weight on the surface. The radius of the planet is R. Find the ratio H/R.

Work:
Let Mp be mass of planet and Ms be the mass of space probe

(true weight) Ft = GMpM/(r+h)^2

(surface weight) Fs = GMpM/r^2

Ft = GMpMs/r^2 - GMpMs/r^2(0.01)

Ft = GMpMs/r^2 - GMpMs/r^2(0.01) = GMpMs/(r+h)^2

i don't know where to go from here

2. Jan 3, 2006

### Tide

Multiply both sides by $r^2$ and write

$$\frac {r^2}{(r+h)^2}$$

as

$$\frac {1}{\left(1 + \frac {h}{r}\right)^2}$$

You should be able to handle the rest.

3. Jan 3, 2006

### neoking77

thank you very much for your help