
#1
Jan2913, 04:59 AM

P: 61

1. The problem statement, all variables and given/known data
I am trying to rearrange formula to make r^2 the subject. 2. Relevant equations 0.05=(2.88/4*1*0.018)(0.05^2r^2) 3. The attempt at a solution I tried to rearrage as : 0.05^2+0.05/2.88/4*0.018 then sqr root of the answer but I dont think it is correct Please help 



#2
Jan2913, 05:36 AM

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Please post your individual individual steps, using parentheses as appropriate. 



#3
Jan2913, 03:23 PM

P: 61

Thank you for your reply,
(0.05^2+0.05)/(2.88/4*0.018)=r^2 this is what I had changed it to .... thanks 



#4
Jan2913, 04:13 PM

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Rearrange of formulaYou start with 0.05=(2.88/4*1*0.018)(0.05^{2}r^{2}). Do you mean 0.05=(2.88/(4*1*0.018))(0.05^{2}r^{2}) or 0.05=((2.88/4)*1*0.018)(0.05^{2}r^{2})? Whichever, post your individual steps, just making one simple change at a time. 



#5
Jan3013, 03:22 AM

P: 61

Ok So I started with :
0.05=(2.88/4*1*0.018)(0.05^2r^2) I wish to make r^2 the subject so , I rearrange to make ; r^2 = (0.05^2+0.05) / (2.88/4*1*0.018) As the first two parentheses are multiply I change it to a divide. I exchange r^2 with the 0.05 and used a plus instead of a minus in the formula. 



#6
Jan3013, 03:47 AM

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hi rad10k!
some people can do these things safely in their head some people can't you can't (you get confused about where to put the brackets) you need to follow haruspex's advice … just do one operation at a time(and not just this question, but always, including in the exam, or you'll make mistakes and lose marks!) 



#7
Jan3013, 04:27 AM

P: 61

This is the equation :
u={∆P/4.Lμ}(R^2r^2) and I wish to find r^2 but a unsure how to rearrange it I thought maybe; r^2=u/{∆P.Lμ}(R^2 ) ?? 



#8
Jan3013, 04:40 AM

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why are you not following our advice?
do it in steps, ie one operation at a time! the first step would be 



#9
Jan3113, 11:30 AM

P: 61

u = {∆P/4.Lμ}(R2r2)
u/{∆P/4.Lμ} = (R2r2) This was arrived by dividing both sides by {∆P/4.Lμ} and cancelling on the right to leave (R2r2) on its own . So then do I need to subtract R2 from both sides cancelling out R2 on the right leaving; u/{∆P/4.Lμ}  R2 = r2 ? I apologise but I am rubbish at rearranging 



#10
Jan3113, 04:27 PM

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#11
Feb113, 06:47 AM

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(caution: you'll always be a bit rubbish, so no matter how much practice you get, and how good you think you've become, you must always do it one step at a time, so that in the pressure of the exam: i] you're less likely to make a mistake ii] if you do make a mistake, at least the examiner can see it's a silly error, and only take off one mark! ) 



#12
Feb113, 10:25 AM

P: 61

Thanks guys :)



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