The wheels of a car have radius 13 in. and are rotating at 650 rpm. Find the speed of the car in mi/h.

Answer 1

This is an exercise in units conversion.

1 ft = 12 inches 1 hour = 60 minutes 1 mile = 5280 ft

one revolution = 2πr = 26π inches

650 rpm = 650 × 26π inches per minute = 60×650×26π = 1014000π inches per hour = 1014000π/12 ft/hr

= 84500π ft/hr /(5280 ft/mile) =16.0038π mph ≈ 50.277 mph