Posted by **Willoby** on Tuesday, January 4, 2011 at 3:41am.

A compact disk is 12 cm in diameter & rotates at 100 rpm when being played. The hole in the center is 1.5 cm in diameter. Find the speed in cm/min of a point on the disk & the speed of a point on the inner edge.

- Plane Trigonometry -
**Damon**, Tuesday, January 4, 2011 at 4:54am
A revolution is 2 pi radians

So it goes w = 200 pi radians/minute

tangential speed = w r = r * 200 pi

at outside

v = 6*200 pi cm/min

at inside

v = 0.75 * 200 pi cm/min

- Plane Trigonometry -
**Willoby**, Tuesday, January 4, 2011 at 5:40am
Hi!Thanks for the answer. Might I ask what w represents?

- Plane Trigonometry -
**Damon**, Tuesday, January 4, 2011 at 5:44am
w is Greek omega (I do not have Greek letters on my keyboard), the angular speed in radians per unit time.

- Plane Trigonometry -
**Damon**, Tuesday, January 4, 2011 at 5:47am
If you have not studied that use:

Circumference at any radius = 2 pi r

Number of circumferences per minute = 100

so at any radius r

speed = 100 * 2 pi r = 200 pi r

- Plane Trigonometry -
**Willoby**, Tuesday, January 4, 2011 at 5:53am
Thanks again!:)

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