# Homework Help: Circular Motion - RPM and Radius question

1. Nov 24, 2012

### PhysicsNoob76

1. The problem statement, all variables and given/known data

A manufacturer of CD-ROM drives claims that the player can spin the disc as frequently as 1200 revolutions per minute.
a. If spinning at this rate, what is the speed of the outer row of data on the disc; this row is located 5.6 cm from the center of the disc?

b. What is the acceleration of the outer row of data?

2. Relevant equations

f = 1/T
V = (2)(pi)(r)/T
a = V^2/r

3. The attempt at a solution

I know that rpm = T/60s, so I did rpm x 60 = T and I got 72,000 s = T (72,000 s for 1 rotation?) That is wrong, I'm not sure how to solve for T...

Last edited: Nov 24, 2012
2. Nov 24, 2012

### tiny-tim

Hi PhysicsNoob76!
if you must do it this way, use 1200 rev per minute = 1 minute per 1200 rev,

so T = time for 1 rev = 1/1200 minutes

but the better way is to convert rev per minute to radians per minute (and then radians per second) …

then you can use speed = radians per second times radius (v = ωr)