Each tire of an automobile has a radius of 125 feet How many

Each tire of an automobile has a radius of 1.25 feet. How many revolutions per minute (rpm) does a tire make when the automobile is traveling at a speed of 85 feet per sec? Round your answer to the nearest tenth.

Solution

circumference of tire is

2* pi * 1.25

= 7.85 ft

speed of automobile = 85 feet / sec

therefore , revelutions per second = 85 / 7.85 = 10.828

changing it to revolutions per minute

10.828* 60 = 649.7 revolutions / minute