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Electric physics question

Could some one help with q13 pls 🙏🏼

http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN14.PDF
I've moved this thread to the Physics Study Help forum where hopefully you'll get more responses :h:
Original post by HG1
Could some one help with q13 pls 🙏🏼

http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN14.PDF

Are you familiar with Coulomb's law? For two point charges with charges q1,q2q_1, q_2 of opposite sign positioned a distance rr apart, there is an attractive force between the two that satisfies:

Force=∣q1q2∣4πϵ0r2\text{Force}=\dfrac{|q_1q_2|}{4 \pi \epsilon_0r^2}

Apply this to the case Force=0.5F,r=20\text{Force} = 0.5F, r=20 to find FF in terms of ∣q1q2∣|q_1q_2|. Then apply it to the case Force=F,r=d,\text{Force}=F, r=d, substitute what you found in the previous step, and rearrange to find dd. :h:

Edit: Oh, almost forgot the :h:.
(edited 7 years ago)
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Original post by Farhan.Hanif93
Are you familiar with Coulomb's law? For two point charges with charges q1,q2q_1, q_2 of opposite sign positioned a distance rr apart, there is an attractive force between the two that satisfies:

Force=∣q1q2∣4πϵ0r2\text{Force}=\dfrac{|q_1q_2|}{4 \pi \epsilon_0r^2}

Apply this to the case Force=0.5F,r=20\text{Force} = 0.5F, r=20 to find FF in terms of ∣q1q2∣|q_1q_2|. Then apply it to the case Force=F,r=d,\text{Force}=F, r=d, substitute what you found in the previous step, and rearrange to find dd. :h:

Edit: Oh, almost forgot the :h:.



Thanks for you're reply would you mind showing me steps of how to get to the answer as I just don't understand the logic ?
Original post by HG1
Thanks for you're reply would you mind showing me steps of how to get to the answer as I just don't understand the logic ?

That formula I gave you *should* look familiar - does it? You really only have to use it twice to get an answer. If you're stuck on the first step, what do you get by putting Force=0.5F\text{Force} = 0.5F and r=20r=20 into that formula? Can you make FF the subject?

Then as you know what FF is, you can use the formula again but with Force=F\text{Force}=F and r=dr=d this time, to get another equation which you can solve for dd.

I'm afraid in general, step-by-step answers are frowned upon in study help. It would be better for you to read my post again and to attempt the steps I outlined. Then post up some working and either myself or someone else will be able to help you further.

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