Asked by Harper

A car is traveling at 40 mph. The radius of its wheels are 14 inches. How many revolutions per minute?


Please show work. I don't understand this.
Answered by bobpursley
change 40mph to inches/minute.

Then, revs= speed/(2PI*r)
Answered by Harper
What is the Pl?
so 42,240/(2 x Pl*14)
Answered by Steve
PI (π) is the ratio of the circumference to the diameter of a circle. So, there are 2π*14 = 28π inches in the circumference of the tire -- that's how far the car goes in one revolution of the tires.

Now it's just a matter of converting mi/hr to rev/min

40mi/hr * 1hr/60min * (5280*12)in/mi * 1rev/28πin = 480 rev/min
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