# Spinning disk

1. Apr 4, 2009

### mattmannmf

Spinning Disk

A disk with a diameter of 0.06 m is spinning with a constant velocity about an axle perpendicular to the disk and running through its center.

a) How many revolutions per second would it have to rotate in order that the acceleration of the outer edge of the disk be 15 g's (i.e., 15 times the gravitational acceleration g)?

HELP: Use the relation between the centripetal acceleration and angular velocity.
HELP: Make sure you use the correct radius.

b) For the frequency determined in part (a), what is the speed of a point half way between the axis of rotation and the edge of the disk?

c) At this same frequency, what is the period of rotation of this "halfway point"?

d) How long does it take a point on the edge of the disk to travel 1 km?

e) Suppose we double the diameter of the disk. We still want the same 15 g acceleration at the outer edge. Let f2 be the number of revolutions per second needed to get that acceleration. What is the ratio R = f2/f, where f is your answer to part (a)? Answer according to the following key:
1 = 0.500
2 = 0.707
3 = 1.000
4 = 1.414
5 = 2.000
6 = none of the above

im not sure what to do

2. Apr 4, 2009

### rl.bhat

Use the relation between the centripetal acceleration and angular velocity.
an you find out the formula for the above?