Calculate Pat's Weight at Earth's Double Radius

[susan__t]

Homework Statement

Pat's mass is 65.5 kg on Earth's surface. What would Pat's weight be at an altitude twice the radius of the Earth

Homework Equations

Fg=G(m1)(m2)/r^2
G = 6.67X 10^-11
F=ma

We are not given the numerical radius of the Earth

The Attempt at a Solution

I tried to manipulate the formula a bit:
(using the gravitational law)
Fg = (65.5)x/ 2^2

And that got me nowhere.
I also know the answer is 71.4N but how you get there is what I don't understand.

 

[hage567]

Fg=G(m1)(m2)/r^2

This equation should work. What are you using for each variable? Look up data you need. It's probably in your textbook somewhere.

 

[Nabeshin]

While hage's solution is valid, I think we know g=9.8 for the surface of the Earth. Therefore, you can look at the equation and see how this force would change as R increases. Think about what is constant and what is changing.