Math CentralQuandaries & Queries


Question from Jules, a student:

Suppose that a tire on a car has an outer diameter of 2,5 feet. How many revolutions per minute does that tire make when the car is travelling 60 miles per hour? (hint:first find the angular velocity in radians per minute.)


Since you want revolutions per minute I would convert the velocity of the car to miles per minute. How many miles/minute is 60 miles/hour? What is that in feet/minute?

The circumference of the wheel is 2,5 π feet so the wheel moves at 2,5 π feet/revolution. Now the units tell you what to do. How do you take your calculation in feet/minute and feet/revolution and obtain a value in revolutions/minute?


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