Math CentralQuandaries & Queries


Question from Crystal, a student:

Suppose a car wheel is 26 inches in diameter.
a) If the tire completes one rotation, how far would the car travel?
b) If the car is traveling at 60 miles per hour, how fast is the car wheel spinning in revolutions per second?

Hi Crystal,

  1. The circumference of a circle of diameter $d$ inches is $\pi \times d$ inches and hence the circumference of the car wheel is $26 \; \pi$ inches.

  2. If the cars is travelling at $60 \frac{\mbox{miles}}{\mbox{hours}}$ then convert miles to inches and hours to seconds to express the speed in inches per second. Since you know that each revolution is $26 \; \pi$ inches divide the speed in inches per second by $26 \; \pi$ to convert to revolutions per second.


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