Is Coulomb's Law the Correct Equation for This Calculation?

[zandbera]

Homework Statement

Nobel laureate Richard Feynman once said that if 2 persons stood at arm's length from each other and each person had 1% more electrons than protons, the force of repulsion between them would be enough to lift a "weight" equal to that of the entire Earth. Carry out an order-of-magnitude calculation to substantiate this assertion.

Homework Equations

F = k |q₁||q₂| / r²

The Attempt at a Solution

I had no idea to do this so i used Coulombs law with q1 = q1 = -e
I used -e because it said there's 1% more electrons so if there's 100 protons, there's 101 electroons and 100 of the electrons would cancel out the protons so the net charge is 1 electron (e). but then It didnt said anything about r so i just guessed and used r = 2 m and then again with r = 1.5m but i got an answer that was x 10^-28 and the answer is supposed to be ~10²⁵

Am I even using the right equation??

 

[xcvxcvvc]

you're using the right equation, but you need to make a better guess on how many electrons each person will have - how much charge to use.

Try to find how many atoms or protons are in the average human body. Then use a charge equal to 1% of that value of protons. If you can only find atoms, use an educated guess as to how many protons a body has from that number of atoms.

googled for you:

"A 70 kg body would have approximately 7*1027 atoms. That is, 7 followed by 27 zeros:

7,000,000,000,000,000,000,000,000,000"

source: http://education.jlab.org/qa/mathatom_04.html (not too reputable but who cares. see if it gives you an appropriate answer)

So for you rcharge, use .01 * 7 * 1027 electrons

also, i measured my arm just now

with hand: ~85 cm
without hand: ~55cm

your distance is way too high

lol 2m = ~6ft. your arm is as tall as a person? :D

 

[zandbera]

Yeah okay I was thinking about that and that makes sense.

And yeah I misunderstood the question. I thought they meant each person was an arms length away so the total distance between them was 2 arms lengths so i used 2(0.75) and 2(1.0)

With that info, I got 6.10 x 10^61. Which is way too high

 

[Redbelly98]

Did you convert the charge units into Coulombs?

 

[zandbera]

Yeah that's where the problem was.

If I use # of electrons = 1.8 x 10^28, then take 1% of that, then multiply that by 1.602 x 10^-19 to convert to Coulombs, square that value, multiply by k, divide by r^2 (r = .85 m) and i get 1.03 x 10^25Thanks!