The radius of a car wheel is 13 inches. How many revolutions per minute is the wheel making when the car is traveling at 40 mph?

Convert 40 mph to inces per minute.

40 x 5,280 feet x 12 inches / 60 minutes =42,240 inches per minute

Circumference =Radius x 2 x Pi

C = 13 x 2 x 3.141592

C=81.68 inches - circumference of the wheel.

42,240 / 81.68 =517.14 ~ 517 - revolutions per minute.