The wheels of a car have radius 10 in and are rotating at 70

The wheels of a car have radius 10 in. and are rotating at 700 rpm. Find the speed of the car in mi/h.

Solution

The circumference of the wheel is 2 * * r = approximately 62.83 inches.

Dividing by the 62.83 inches by 12 converts that into 5.24 feet.

Since the wheel is rotating at 700 rpm, it is rotating at 60 * 700 = 42,000 rotations per hour.

Since each rotation covers 5.24 feet that total speed is 42,000 * 5.24 per hour. Multiplying those two numbers we get:
220080 feet per hour.

Since there are 5280 feet to a mile, when we divide 220080 by 5280, we convert from 220080 feet per hour to 41.68 miles per hour.