# Quick help with NUCM of a disc

1. Oct 11, 2009

### dsimpson

1. The problem statement, all variables and given/known data
a disc drive at rest is powered up and accelerates according to alpha=alpha(i)sin(bt). this lasts for 1.66 seconds after which it no longer accelerates. alpha(i)=506 rad/s^2 b=1.89 radius of disc=3.9cm. After the disc is done spinning up what is the centripetal acceleration of the edge of the disc.

I take this to mean the acceleration at the time of 1.66 because the answer isn't zero. Don't i just plug the time into my equation?

2. Oct 11, 2009

### Soveraign

Centripetal acceleration is acceleration directed towards the center of circular motion. So this is usually

$$a_c=-\omega^2 r$$

or
$$a_c=-\frac{v^2}{r}$$.

In either case you need to know how fast the disc is rotating (and its radius). So how would you determine how fast the disc is turning after 1.66 seconds?