Solving Basic Electricity Questions - 4q Net Charge

[duki]

Hey everyone,

There is a question in my book that asks if three particles touch and are then separated (A- +5q, B - -q, C - 0) what is the net charge? I know the answer is 4q, but it also states the following:

Particle C touches A and is removed. Particle C then touches B and is removed. What is the final charge on C? I got 1.333... but the answer in the back of the book says 1.5. Am I doing something wrong?

 

[Integral]

If you could explain how you got 1.33... we could help find where you went wrong.

 

[duki]

i did net charge 4q / 3

 

[berkeman]

The question is a little ambiguous. You are correct if the first thing you do is touch them all together, as in your question #1. However, the book's answer is correct if you start again in question #2 with the balls having their initial (different) charge states. Do the problem again with that assumption, and you'll get the correct answer.

 

[duki]

ok. It works like that. I wonder why they didn't word it correctly. It's worded to do it how I did the first time...

Anyways, thanks for your help!