Difference in Planet Mass

**Serena_Greene** · Oct4-05, 08:55 AM

I think I have done this problem correctly,

The mass of a robot is 6680 kg. This robot weighs 3070 N more on planet A than it does on planet B. Both planets have the same radius of 4.00 x 10^8. What is the difference Ma - Mb in the masses of these plantes?

I used this equation F = G * (m1*m2)/(r^2)
F = 3070 N
m1 = robot
mb = extra mass of planet A
r = 4.00 x 10^8

3070 = 9.673 x 10^-11 * 6680m2/ (4.00 x 10^8)^2
3070 = (2.786 x 10^-24)m
1.1019 x 10^27 = m

Is this correct or do I have it totally wrong?

-Serena

**Päällikkö** · Oct4-05, 09:07 AM

I got a different answer, you seem to have typed it wrong into your calculator, the equation's the same as mine.

EDIT: Never mind. I had used the gravitational constant you typed, which was wrong :). I got the same answer now.

**El Hombre Invisible** · Oct4-05, 09:36 AM

I tried it, though not using your technique, and your answer seems correct. Same answer from two different methods is usually a good sign.

**El Hombre Invisible** · Oct4-05, 09:37 AM

Although your answer should be in kg, not m.

**Serena_Greene** · Oct4-05, 06:07 PM

Thanks!!

I just wanted to make sure before I typed it into GradePlus. It was correct (I had already used up a try as I couldn't get the entire number in, but found out I could use Exponents) I asked my Physic teacher if I did the problem correctly and he started to do the problem, and he couldn't do the problem.

-Serena