# Homework Help: Magnitude of Forces exerted by charges.

1. Aug 25, 2009

### genu

1. The problem statement, all variables and given/known data
A charge q1 = 4.0 μC is at the origin and a charge q2 = 6.0 μC is on the x axis at x = 3.0 m.

Find the magnitude of the force exerted on q1. Give your answer in N rounded to 3 decimal places.

Find the magnitude of the force exerted on q2. Give your answer in N rounded to 3 decimal places

2. Relevant equations

F=(k(q1*q2))/r^2

3. The attempt at a solution
I converted μC to C
and I got 23.973N for the first part. (isn't this too much force for a charge?)
The second part, shouldn't the force be the same?

2. Aug 25, 2009

### kuruman

Yes, in the second part the force should be the same. Can you explain why?

3. Aug 25, 2009

### genu

q1 = 4.0 μC = 4.0 * 10^-9 C
q2 = 6.0 μC = 6.0 * 10^-9 C

here is what I did
F = (8.99 * 10^9 * 4.0 * 10^-9 C * 6.0 * 10^-9 C)/3.0^2 = 23.973N

Now that I think about it, the difference between the 2 questions should be the direction of the force, but the same magnitude.

4. Aug 25, 2009

### kuruman

Redo your calculation for two reasons

1. 1.0 μC = 1.0 * 10-6 C
2. Just by looking at the powers of 10 and your answer, it is clear that you forgot to multiply by the second 10-9.

5. Aug 25, 2009

### genu

oh...I see, thank for pointing that out.

As far as the signs go, do the answers have different signs?

Although, they don't specify as to whether the charges are positive or negative.

6. Aug 25, 2009

### kuruman

Signs don't matter here. You are asked to find magnitudes and these are always positive.