Posted by **Norah** on Sunday, August 29, 2010 at 3:56pm.

A car is moving at a rate of 65 miles per housr and the diameter of it's wheels is 2.5ft. Find the number of revolutions per minute the wheels are rotating.

I have no idea where to begin on this question. How do you find rev per min?? Can someone walk me step by step how to answer a problem this?

- L PreCal -
**drwls**, Sunday, August 29, 2010 at 4:05pm
First convert miles per hour to feet per second.

65 mph = 95.3 ft/s

The rotation rate of the wheels in radians per second, w, is

w = (speed)/(radius) = (95.3 ft/s)/(1.25 ft)

= 76.3 radians/s

Convert that to rpm by multiplying by

(60 s/min)*[1/(2 pi)] rev/rad)

729 rpm

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