linear speed

Question

On a carousel, the outer row of animals is 21 feet from the center. The inner row of animals is 9 feet from the center. The carousel is rotating at 3 revolutions per minute. What is the difference, in feet per minute, in the linear speeds of the animals in the outer and inner rows? Round to the nearest foot per minute.

Answer 1

The Circumference of circle is:

     C = πd    (because the definition of π = C/d)

     C = 2πr

 

"The carousel is rotating at 3 revolutions per minute"    means

   linear speed = 3C feet/min

 

Mow, use the two distances to find the difference in the linear speed:

    outer row      -      inner row

  3*2*π*21       -      3*2*π*9

        6π(21-9)

         72π

        226 ffet/min    (rounded)

Answer 2

Outer row travels 7π / min  (21π / 3)

Inner row travels 3π / min  (9π / 3)

 

What is the difference?