Homework Help: Order of magnitude problem involving the force of repulsion between two persons

1. Aug 27, 2012

StrawHat

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

2. Relevant equations

$\vec{F}$ = k$\stackrel{q1q2}{r^{2}}$

3. The attempt at a solution

6.022e23*(0.505) = 3.041e23C <-- electrons
6.022e23*(0.495) = 2.981e23C <-- protons
3.041e23 - 2.981e23 = 6e21C <-- the difference between the two charges
$\vec{F}$$_{e}$ = (9e9Nm$^{2}$/C$^{2}$)(6e21C)$^{2}$ / 2.25m$^{2}$
$\vec{F}$$_{e}$ = 1.44e53 N

2. Aug 27, 2012

CAF123

Re: Order of magnitude problem involving the force of repulsion between two persons..

Given that the force of repulsion is similar to the gravitational force exerted on an object with a mass the size of earth, you should expect F ~ 1025N.

There is an identical thread here:

3. Aug 27, 2012

StrawHat

Re: Order of magnitude problem involving the force of repulsion between two persons..

The answer gives me this error: "Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error."

4. Aug 27, 2012

nasu

Re: Order of magnitude problem involving the force of repulsion between two persons..

What is the answer that you put in the box?

5. Aug 27, 2012

StrawHat

Re: Order of magnitude problem involving the force of repulsion between two persons..

I put in F~10 25N.

6. Aug 28, 2012

voko

Re: Order of magnitude problem involving the force of repulsion between two persons..

How do you get the number of protons?

7. Aug 28, 2012

nasu

Re: Order of magnitude problem involving the force of repulsion between two persons..

I would consider trying to enter 26 in the box. Depending on how you estimate, you may get 10^26. And the "weight" of the Earth is also of the order 10^26 (6x10^25).