# How much does a person weigh on Mount Everest?

1. Nov 7, 2010

### droopster

1. The problem statement, all variables and given/known data

If a person has a mass of 68kg, how much does he weigh on the top of mount everest (8488km above sea level?
Given: m=68kg, d=8488m

2. Relevant equations

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

3. The attempt at a solution

I tried figuring out the new radius. Once i get the radius i enter all the data and rearrange the formula to get m2 by itself.
Fr^2/Gm1 = m2

My problem is getting the new radius.

Last edited: Nov 7, 2010
2. Nov 7, 2010

3. Nov 7, 2010

### droopster

Sorry, the old radius is the basic radius in the original formula. Its just r^2. But since im dealing with a new altitude doesn't it change?

4. Nov 7, 2010

### Staff: Mentor

You didn't understand my question. I'll take another tack. How much does the person weigh at sea level? Why?

5. Nov 7, 2010

### droopster

He weighs 668N at sea level. Why? Well His mass multiplied by gravity gives me the weight.

6. Nov 7, 2010

### Staff: Mentor

What about Newton's law of gravity? Does that not apply at sea level?

7. Nov 7, 2010

### droopster

As long as an object is at or near the surface of the celestial object and we know the value of g the gravitational field strength at the surface of the celestial body, we can use F= mg to find the weight of the object

8. Nov 7, 2010

### Staff: Mentor

Newton's universal law of gravitation, F=GMm/r2, is not called universal just on a whim.

In other words, it applies at sea level as well as atop Mt. Everest.

9. Nov 7, 2010

### droopster

But the answers are different. My answer book tells me that the weight on the surface of the earth is 668 newtons and 664 newtons on mount Everest.

10. Nov 7, 2010

### droopster

Whoops, was i not supposed to read that xD?

Last edited: Nov 7, 2010
11. Nov 7, 2010

### Staff: Mentor

No, you were not supposed to see that.