Calculating Gravitational Field Constants for Mars, Jupiter, and Mercury

[Dyna]

1. Calculate the gravitational field constants for the following:
Mars (r=3.43 x 10^6m , m= 6.37 x 10^23 kg)
Jupiter (r= 7.18 x 10^7 , m = 1.90 x 10^27kg)
Mercury (r=2.57 x 10^6m , m= 3.28 x 10^23 kg)
2. F = mg
Fg = Gm1m2
r^2
3. So i tried subbing these given masses into the second equation but it does not give me the correct answer.
Am i not using the correct equation?
I only just learned this in school on Friday and it was quite confusing as to what i should be using to find my answers.
The answer key says:
Mars: 3.61 m/s^2
jupiter: 24.6m/s^2
mercury: 3.31m/s^2

 

[planck42]

Use Newton's Second Law of Motion in conjunction with Newton's Universal Law of Gravitation.

 

[merryjman]

In other words, since you're only given one mass (the planet's mass, call it m2), you've got to get rid of the second mass m1. You have the right equation to do this, F=mg. If you sub that into the left side, one of your m's will drop out, and you're left with g on the left side, and the correct answer on the right :)