Static Electricity and particles

1. Jan 31, 2009

me_and_you

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

Particles of charge +70, +48, and -80 $$\mu$$C are placed in a line, in the previous order. The center one is .35 m from each of the others. Calculate the net force on each charge due to the other two.

2. Relevant equations

F=kq1q2/ d2

3. The attempt at a solution

I found the force between each but according to my teacher im not doing this correctly could someone please tell me how i should go about doing this problem.

2. Jan 31, 2009

LowlyPion

Draw a diagram. Consider one charge at a time.

The ones on the end will be .35 and .7 distant from the other 2 respectively.

Be careful with the signs. Be careful with the units.

Be careful that you have taken care to note the direction of the force in each equation. (+,-) attracts and same sign repels.

Since forces are vectors then you must take that into account when you add them by superposition.

3. Jan 31, 2009

me_and_you

I thought thats what I was doing but after trying again i got the same wrong answer, I'm so confused about wht i should do with this problem!

4. Jan 31, 2009

LowlyPion

Show your calculation then for the middle charge.

5. Feb 1, 2009

me_and_you

F1= (9x109)(70 x 10-6)(48x10-6)/ .352

this equals: 246.86

F3= (9x109)(-80 x 10-6)(48x10-6)/ .352

this equals: -282.1

Then i did
(246.862)+ (-282.12)= Q2

Q= 374C

but according to my teacher this is wrong... can you tell me what it is that im doing wrong?