a common speed for an electric motor is 3450 revolutions per

a common speed for an electric motor is 3450 revolutions per minute. saw blads of various diameter can be attached to such a motor. determine the linear velocity in mi/hr for a point on the edge of a blade with 12 in

Solution

The circumference of a circle with a DIAMETER of 12 inches is pi*(12 inches) = 12*pi inches.
(Remember that Circumference = 2*pi*radius = pi*diameter)

And the point on the blade travels 12*pi inches (around the circle) 3450 times per minute.

12*pi inches * 3450 / 1 minute
= 41400*pi inches/minute

41400*pi inches/minute * 60 minutes/hour * 1 foot/12 inches * 1 mile/5280 feet
= 123.2 miles/hour