Static Electricity and particles

[me_and_you]

Homework Statement

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.

Homework Equations

F=kq₁q₂/ d²

The Attempt at a Solution

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

 

[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.

 

[me_and_you]

I thought that's 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!

 

[LowlyPion]

Show your calculation then for the middle charge.

 

[me_and_you]

Show your calculation then for the middle charge.

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 I am doing wrong?