math
posted by Derby .
Your roommate is working on his bicycle and has the bike upside down. He spins the 68.0cm diameter wheel, and you notice that a pebble stuck in the tread goes by three times every second.
What is the pebble's speed?
What is the pebble's acceleration?

speed=distance/time=PI*68cm/.3333sec
acceleration= speed^2/radius
of course, radius is still half diameter. 
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