A car is traveling at 42 mph. if its tires

have a diameter of 27 inches, how fast are

the car's tres turning? Express answer

in revolutions per minute.

522.9 revolutions / min

Step-by-step explanation:

Given Diameter, D = 27 inches

Circumference, C = πD = 3.142 x 27 = 84.82 inches

(recall 1 mi = 63360 in)

Car speed is 42 mph = 42 mph x 63,360 inches / mile = 2,661,120 inches / hr

(recall 1 hour = 60 min)

Hence car speed becomes

= 2,661,120 inches / hr : 60 min/hr

= 44,352 inches / min

Number of revolutions / min

= speed in inches/min : circumference

= 44,352 : 84.82 = 522.9 revolutions / min