# Simple problem of gravitational field

1. Aug 19, 2009

### skydiver

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

What is the magnitude of the gravitational field at the surface of a neutron star whose mass is 1.80 times the mass of the Sun and whose radius is 9.3 km?

2. Relevant equations

g = GM/r2

3. The attempt at a solution

G is ofcourse 6.67x10^-11
r^2 is 8.649x10^7 m

Now I don't know what to take as mass. I took just 1.8 and it didn't work. I just took the mass of sun as 1.9x10^30kg and it didn't work and I also tried the product of those two.
What am I missing?
Okay I tried all I could but I am now stuck. Can someone help me. Thanks so much.

2. Aug 19, 2009

### LBloom

It appears you have everything you need. If the nuetrons star's mass is 1.8 times the suns, you should just times the suns mass by 1.8, which it appears you've done.
I would just check everything is in SI units and maybe reread the question.

3. Aug 20, 2009

### skydiver

Thanks, I double checked everything yet nothing seems to work.

4. Aug 20, 2009

### skydiver

Apparently the STUPID hw system does not recognize x 10^y format yet the only error it gives is incorrect answer.

5. Aug 20, 2009

### LBloom

if you don't mind, can you tell me what you've been getting as the answer? Maybe i can check if its just a computational error
also, it sounds like its a multiple choice qu, so maybe you should check their units too? Not really sure what the problem is.

6. Aug 20, 2009

### skydiver

We have an online system where you input the answer and it says if it's correct or not. If it's correct you get the points.
2748510000000 m/s^2 is the answer and the system recognized it (ie it's correct)
I was inputting the number as 2.748 x 10^12 and hence the system said incorrect answer which is poor design of the system IMHO

And it's not multiple choice

7. Aug 20, 2009

### LBloom

hmm, i got a similar answer, but i used a different measurement for the sun's mass (through google). I've never used the system you've described, but it might help to try looking up the sun's mass to a greater accuracy. Even if you were to round it, it looks closer to 2x10^30 than 1.9. Other than that, i'm not sure what else there is besides fiddling with the numbers
I'd help you more, but I gotta get some sleep, its like 2 in NY. good luck with that system though.