# Solve rpm in rotational motion problem

1. Mar 14, 2008

### adca14

1. The problem statement, all variables and given/known data
How fast (in rpm) must a centrifuge rotate if a particle 7.0 cm from the axis of rotation is to experience an acceleration of 100,000 g's?

My variables
radius= 7 cm or .07m
radial accel= 100,000 g's or 980,000m/s^2 or 98,000,000cm/s^2
V= I think I need this to get w
w= ? I think I need to solve this to get rpm
rpm= ? this is what I want

2. Relevant equations
radial accel = v^2/r
v= rw

3. The attempt at a solution
980000/.07 = 68,600

$$\sqrt{}68600$$/.07= 261.9
261.9/.07 = 3,741 rpm

whether i set everything as meter or centimeter, I still get the same answer. I check the back of the book and it says 3.6x10^4 or 36,000rpm
1. The problem statement, all variables and given/known data

Any help would be appreciated.

2. Mar 14, 2008

### Dick

Your answer is correct but it's in radians per second. rpm is revolutions per minute. A revolution is 2*pi radians and a minute is 60 seconds. Can you convert it to rpm?

3. Mar 15, 2008

### adca14

thank you, I did:
3741rad*60=224,460
224,460/2*pi=35,723rpm or 36000rpm if I round up. Thanks again!

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