# Planet and speff problem find mass

1. Nov 16, 2011

### physicsgurl12

1. The problem statement, all variables and given/known data
The weigh tof spaceman speff, soley due to the gravitational pull of planet x at its surface is 389N. If he moves to a distance of 1.86*10^4km above the planets surface his weight changes to 24.31N. What is the mass of planet xif speffs mass is 75 kg.

2. Relevant equations

f=ma
f=gm1+m2/r^2

3. The attempt at a solution
i know the answers is 2.96*10^24 kg. nut idk how to get it

2. Nov 16, 2011

### SteamKing

Staff Emeritus
I would double check your second equation.

3. Nov 16, 2011

### physicsgurl12

it m1*m2

4. Nov 16, 2011

### physicsgurl12

what else?? im still not getting it

5. Nov 17, 2011

### Redbelly98

Staff Emeritus
Use the F=G·m1·m2/r2 equation, and plug in the given information. There are two sets of information, so you would get two equations:

(1) 389 N = G · __ · __ / __
(2) Use the other weight given in the problem to set up the second equation