Physics help please.. compact disk?

K

Khan

New member
Unlike the older vinal records which rotated at a constant ω of 33.3 rotations per minute (rpm), compact disks vary their rotation speed during the playing period. A certain CD has a diameter of 12cm and a playing time of 77 minutes. When the music starts, the CD is rotating at 480 rpm. At the end of the music, the CD is rotating at 209 rpm.

a) What is the final rotational velocity of a point on the very outer edge of the disk?

b) What is the final rotational velocity of a point that is half way between the center of the disk and the outer edge?

c) What is the final tangetial speed of a point on the very outer edge of the disk?

d) What is the final tangential speed of a point half way between the center of the disk and its outer edge?

e) What is the magnitude of the average angular acceleration of the disk during this playing period?
 
a) What is the final rotational velocity of a point on the very outer edge of the disk?

-Well it depends really on which method of measurement you utilise. Is it Del a Queefs method or perhaps Fernando Goatse? Either one will provide you with a near enough accurate answer but for an absolute truth one must ask oneself, Who asked the question? You? Hardly! It was me who posted this and you are the one answering. Confused? Then perhaps Physics is the wrong area of expertise for you


b) What is the final rotational velocity of a point that is half way between the center of the disk and the outer edge?

-Well if its half way between the center of the disk then why not look to the center of yourself for the answer? It's there, just waiting for you. Dont be afraid of what you may find, the truth shall set you free.

c) What is the final tangetial speed of a point on the very outer edge of the disk?

-Well thats OBVIOUSLY a trick question because as we all know tangetial speed is nothing more than big word talk for cheese-it.

d) What is the final tangential speed of a point half way between the center of the disk and its outer edge?

-HA! Trying to trick me again are you? Like i said before cheese-it

e) What is the magnitude of the average angular acceleration of the disk during this playing period?

-6 magnitudes
 
decide if yu are talking about the tangential velocity of a point on the disk or the angular vel.

V tan = R v rotation
v rotation in radians /sec
1 rotation/sec = 2Pi omega the angular rotation.

radian measure can get confusing, be sure to understand it
e-m my icon for more help
 
decide if yu are talking about the tangential velocity of a point on the disk or the angular vel.

V tan = R v rotation
v rotation in radians /sec
1 rotation/sec = 2Pi omega the angular rotation.

radian measure can get confusing, be sure to understand it
e-m my icon for more help
 
This one is a really interesting question, and I've had an answer prepared for it for years. I KNEW this would come up some day:

a) The disk is round,
Like a coin on the ground,
It plays in my heart,
Music better than farts,
I laugh and I cry,
Wet things come from my eye,
But it won't get me down,
I just stand upside down,
In the blink of an eye,
I no longer cry,
I just rain on the ants,
As they fall from my pants.

b) Roataional velocity is dependent on mass, circumference and the disposition of the gremlins turning the mechanism inside the machine you are using. For example, I once played some music they didn't like so much - Phil Collins I believe - and so they worked their little butts off to get it over with as quick as they could. Thay slowed down to about 200rpm at the middle of the disk but found a last drop of energy when 'True Colours' was played, they hate that song. It sped up to over 1000rpm!

c) I very much like donuts, they're shaped like disks, the hole in the middle and all. Some people say the universe is the shape of a donut. Intriguing, isn't it?

d) No eggs in here sir, the chickens are on strike.

e) I wish to draw your attention to my leg. I'm bringing it down upon a donut. I don't like them anymore. One bit me, it said I was taking advantage of it in a drunken state, but it asked me to do those things! I swear! You ain't got nothin' on me! I'm as free as a bird, ya hear me? A bird I tell ya! And you know how you catch a bird? You don't!
 
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