Quandaries and Queries



a rock on a 4' string is rotated at 80 rpm. what is the linear speed in feet per second? in miles per hour? (could you go into detail as to how the anwser was reached)




I can get you started. The rock moves around a circle of radius 4 feet. The circumference of a circle is 2pi times the radius and hence in each revolution of the circle the rock travels

2 pi 4 = 8 pi feet.

The rock is moving around the circle 80 times per minute and hence it is travelling at

8 pi 80 = 640 pi feet per minute.



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