L PreCal
posted by Norah on .
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?

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