Answer:
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
