Some electric charge and force questions on how to set them up

[kevinlikesphysics]

ok here are the question i just need to know how to set them up and work them out this is due tomorrow night at like 12 oclock and my teacher hasnt explained it very well can someone just work it out for me in the equation or just eplain what to do or maybe do one anything will help thanks alot

3. [SFHS99 17.P.17.] At the point of fission, a nucleus with 92 protons is divided into two smaller spheres, each with 46 protons and a radius of 5.4 10-15 m. What is the repulsive force pushing these two spheres apart?


4. [SFHS99 17.P.18.] What is the electric force between a glass ball with 2.5 µC of charge and a rubber ball with -4.0 µC of charge when they are separated by 5 cm?

5. [SFHS99 17.P.19.] An alpha particle (charge = +2e) is sent at high speed toward a nucleus (charge = 69e). What is the electric force acting on the alpha particle when it is 2 10-14 m from this nucleus?

6. [SFHS99 17.P.20.] Three positive point charges of q1 = 4.5 nC, q2 = 6.0 nC, and q3 = 1.5 nC, respectively, are arranged in a triangle, as shown in Figure 17-25. Find the magnitude and direction of the electric force on the 6.0 nC charge.
___N
___° (counterclockwise from the positive x axis)
image - http://www.webassign.net/sfhs99/17-25alt.gif

7. [SFHS99 17.P.21.] Three point charges lie along the y-axis. A charge of q1 = 9.2 µC is at y = 6 m, and a charge of q2 = 7.4 µC is at y = -4 m. The net electric force on the third charge is zero. Where is this charge located?

8. [SFHS99 17.P.22.] A charge of 3.5 nC and a charge of 5.2 nC are separated by 40.0 cm. Find the equilibrium position for a -6 nC charge.
m (from the 3.5 nC charge)

9. [SFHS99 17.P.39.] Calculate the net charge on a substance consisting of a combination of 8.0 1013 protons and 2.0 1013 electrons.


there are some more but i got them right already

 

[Astronuc]

The magnitude of charge on a proton and electron is the same, 1.602 x 10^-19 C. Protons are +, and electrons -.

However, please show your work before asking for assistance.

In the case of spheres (e.g. two nuclei) touching, try using twice the radius as the separation.

 

[kevinlikesphysics]

thanks i got it wrong thought the reason id ont have work is because i dontk nwowhat equeations to use i have no clue what I am doign and its an online test so i don't want to quess i have been using f = k q1q2 /r(squared)

but i keep getting the #3 wrong along withsome of the other i just need to know one step by step then i can figure it out and my book is horrible is give background info on how it was discovered by not how to do any of it

for # 3 i did f = 9e9 * 1.2e-19 * 1.6e-19 /(5.4e-15 * 2)squared

can you tell me what i did wrong