# What is the gravity of a planet 2 times the radius and 3 times the mass of earth

1. Oct 3, 2012

### cmbswim89

what is the gravity of a planet 2 times the radius and 3 times the mass of earth

2. Oct 3, 2012

### SammyS

Staff Emeritus
Re: gravity

Hello cmbswim89. Welcome to PF !

Do you mean, "What is the acceleration due to gravity on the surface of a planet 2 times the radius and 3 times the mass of earth?"

Show us what you have tried, and where you're stuck so we can help you.

3. Oct 3, 2012

### cmbswim89

Re: gravity

well the problem states a person weighs 540N on earth and asks how much he weighs on a planet 2 times the radius and 3 times the mass. i have tried putting that data into the gravitational force equation but multiplying earths mass by 3 and radius by 2 but i don't get any of the multiple choice questions i have

4. Oct 4, 2012

### SammyS

Staff Emeritus
Re: gravity

What equation are you putting the mass & radius into ?

What do you get?

5. Oct 4, 2012

### cmbswim89

Re: gravity

F=G(3(m1))(m2)/2r2 so it looks like that with m1 as earths mass and r as earths radius and i get 793.18N

6. Oct 4, 2012

### SammyS

Staff Emeritus
Re: gravity

Are you using (2r)2 or 2(r2) in the denominator?

7. Oct 4, 2012

sr^2 sorry