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Revs per min from metres per second 
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#1
Jun606, 04:14 AM

P: 66

okay so here is the problem and here is wat I did!
I am just tryin to study up for exams now... and this is one of the problems! A sample of blood is placed in a centrifuge of radius 17.5 cm. The mass of a red corpuscle is 3.00×1016 kg, and the magnitude of the force required to make it settle out of the plasma is 4.08×1011 N. At how many revolutions per second should the centrifuge be operated? Basically wat I did is found the velocity in metres per second first which I find is 154m/s which I found by usin F=(mv^2)/r But here is the simple problem that I am confused about... how do I change this to revs/sec. Is it somethin to do with C=2PIr, thats all I can think of! Thanks for your help! 


#2
Jun606, 04:29 AM

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P: 9,772

[tex]F = m\alpha[/tex] Where alpha is centripetal acceleration and [itex]\alpha = r\omega^2[/itex] where omega is angular velocity (rads/s). Thus; [tex]\fbox{F = mr\omega^2}[/tex] You method is completely valid, but is a bit long winded . You can convert radians per second into revolutions per second by dividing by [itex]2\pi[/itex]. 


#3
Jun606, 04:46 AM

P: 66

okay I did that and now I am so far off... I did 123686.127rev/sec.
so wat I did was w^2=f/mr but then I got that in rads per second =7.77E5 which is bigger then I expected. So I then divided by 2*PI... then it was wrong... the answer is meant to be 140.3 


#4
Jun606, 04:51 AM

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Revs per min from metres per second



#5
Jun606, 05:02 AM

P: 66

thanks a lot I appreciate it, I thought I did sqaure root the answer but now I got the right answer.! ;P



#7
Jun606, 08:31 AM

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AM 


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