eletrcon physics problem?

Question

Calculate the magnitude of the force between two 4.05 µC point charges 9.8 cm apart.

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How many electrons make up a charge of -75.0 µC?

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If someone can solve any question that would be a great help..... thanks

What is the magnitude of the force a +17 µC charge exerts on a +2.8 mC charge 37 cm away?

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Two charged dust particles exert a force of 2.7 10-2 N on each other. What will be the force if they are moved so they are only one-fourth as far apart?

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Two charged spheres are 15.0 cm apart. They are moved, and the force on each of them is found to have been tripled. How far apart are they now?

Answer 1

1. F=k(q1 q2)/r^2 (see ref 1)
2. Number of electrons=(q total) /(charge per electron) (see ref 2)
3. F=k(q1 q2)/r^2
4. Using the force and the distance compute k(q1 Q2) then compute F at 1/4R
5.since F=k(q1 q2)/R^2
So R2=sqrt(k(q1 q2)/3F) and F=k(q1 q2)/R1^2
Then R2=sqrt(k(q1 q2)/3[k(q1 q2)/R1^2])
R2=sqrt[ R1^2/(3)]=
R2=R1 sqrt[1/3)]=15 (0.577)= 8.66 cm