Centripetal Force acceleration

[luap12]

1. A computer is reading data from a rotating CD-ROM. At a point that is 0.0330 m from the center of the disk, the centripetal acceleration is 264 m/s2. What is the centripetal acceleration at a point that is 0.0702 m from the center of the disc?



2. a_c=v²/r



3. So my thoughts here are that it should be assumed that the velocity is constant. So I need to fine that velocity for the known radius and acceleration with the equation about. After I find the velocity, I can plug it into the equation with the new radius and find the acceleration that way.
a_c=v²/r
264=v²/.0330
v²=8.712 m/s
v=2.95161 m/s

then plugging that into the equation with the other radius
a_c=v²/r
a_c=8.712/.0702
a_c=124.10256 m/s²

This is not the right answer for my homework though. Not sure what I am doing wrong. Anyone know?

 

[praharmitra]

well...the disc is rotating...so v is NOT constant. However, for constant rotation, angular velocity is constant. Use the relation between that and v, and modify your equation for acceleration.

 

[luap12]

ok, I understand now that the velocity is not constant. I don't believe we have covered angular velocity yet in class, unless I am just overlooking it. How do you do that? I did set up a proportion though with the velocity and radius and got it correct.

 

[LowlyPion]

Maybe this will help?
http://hyperphysics.phy-astr.gsu.edu/hbase/rotq.html#avel