Using Coulombs Law-Comparative Analysis

[wilson_chem90]

Homework Statement

Look back at the Example in the Using Coulombs Law-Comparative Analysis section. Calculate the magnitude of F2 if both changes occurred simultaneously-that is, if the distance between the charges doubled and the size of once tripled, while the size of the other doubled.

This is the original example:

If the electrostatic force between two charges is 6.0 x 10^-8 N, what effect would each of the following changes have on the magnitude of the force?
1) the distance between the charges is doubled
2)One charge is doubled and the other is tripled

Solution:
1)
F2 = (6.0x10^-8 N)xr1 / (2r1)^2
= (6.0x10^-8 N) / 4
= 1.5 x 10^-8 N

2) q1=2q1
q2=3q1

F1/F2 = q1q2/q1q2

(6.0x10^-8 N)/F2 = q1q2 / (2q1)(3q2)

F2 = (6.0x10^-8N)(6)
= 3.6 x 10^-7 N

This is the solution to the example!

Homework Equations

The Attempt at a Solution

r' = 2r

q1' = 3q1

q2' = 2q2

First i set F1/F2 = (q1q2/r1^2) / ((3q1)(2q1)/2r1^2)

Then after i rearranged it and canceled out q1q2 and r1
i ended up with the equation F2 = 6F1/4

then i put in F1

therefore:

F2 = 6(6.0 x 10^-8N) / 4
= 9.0 x 10^-8 N

Therefore, the magnitude of F2 is 9.0 x 10^-8 N

I don't think i rearranged it correctly, can someone please confirm. Thank You

 

[kuruman]

... i ended up with the equation F2 = 6F1/4...

It looks like you combined parts (1) and (2) together. The changes are made independently, so the answer to part (1) is F₁/4 and the answer to part (2) is 6 F₁.

 

[AClass]

It looks like you combined parts (1) and (2) together. The changes are made independently, so the answer to part (1) is F₁/4 and the answer to part (2) is 6 F₁.

Would that mean that F2 is (3/2) of F1? if they were combined.

Because I obtained the same answer.

 

[cupid.callin]

Why do you think that your answer is wrong?

It seems correct to me.