# Gravitational force

1. Mar 26, 2007

### Aikenfan

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

I just need help with part 3, if anyone can help me, i don't really know what to do

2. Relevant equations
F=k(q1)(q2)/r^2

3. The attempt at a solution

2. Mar 26, 2007

### giritrobbins

It is simple Newtonian Gravitation.
F=G(mp)^2/r^2

mp=mass of a proton
G=Universal graviational constant
mp is squared because it is two protons, otherwise it would be m1 and m2

3. Mar 26, 2007

### Aikenfan

G is constant, but i am unsure of how to get mp

4. Mar 26, 2007

### giritrobbins

The mass of a proton is constant. It should be locatable in any physics book or going to google and typing mass of a proton

5. Mar 26, 2007

### Aikenfan

Okay, i got: 16726E-27^2 * G / .0071^2
= 3.6627E-52

Last edited: Mar 26, 2007
6. Mar 26, 2007

### Aikenfan

i submitted it but got it wrong, but i have a few more tries to get it right, what did i do wrong?

7. Mar 26, 2007

### hage567

That’s 1.6726x10^-27 kg for the mass of a proton, right? It looks like you were missing the decimal in there.

8. Mar 26, 2007

### Aikenfan

now i got 3.66e-60

9. Mar 26, 2007

### hage567

Did it work? It should.

10. Mar 26, 2007

### Aikenfan

it says it is wrong, not sure why though, i double checked. it seems like it should be right

Last edited: Mar 26, 2007
11. Mar 26, 2007

### hage567

Well, I get 3.70x10^-60 N, so maybe it is a rounding issue? I don't know how picky web programs are about that kind of thing. I can't see why the answer would be wrong.

12. Mar 26, 2007

### Aikenfan

i have 1 guess left, i will try 3.70x10^-60 N

13. Mar 26, 2007

### Aikenfan

hmm maybe not, one of my previous guesses was 3.69e-60, that probably should have been correct

14. Mar 26, 2007

### hage567

Sorry, I just am not able to see what could be wrong with that calculation.

15. Mar 26, 2007

### Aikenfan

thank you for all of your help

Last edited: Mar 26, 2007
16. Mar 26, 2007

### Aikenfan

i got it incorrect, but the answer was 3.811e-60
have no idea how they got that, ill have to check with my teacher because i still think the other answer is correct, maybe it is a mistake

17. Mar 26, 2007

### hage567

A different value for the proton mass was probably used. If I work it out backwards I get 1.697x10^-27 kg for the mass. Not the right one as far as I'm concerned.

18. Mar 26, 2007

### Aikenfan

i think i will ask my teacher, maybe she will give it to me
thank you very much for all of the help!

19. Mar 26, 2007

### neutrino

It may be, just may be, that the program assumes the value of the proton mass to be 1.67e-27 - just to two decimal places.