SOLUTION: A steel bar with a radius of 6 inches is being ground in a lathe. The surface speed of the bar is 29 ft/min.How many revolutions will the bar make in 51 sec?

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Question 1199528: A steel bar with a radius of 6 inches is being ground in a lathe. The surface speed of the bar is 29 ft/min.How many revolutions will the bar make in 51 sec?
Answer by ikleyn(52847) About Me  (Show Source):
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A steel bar with a radius of 6 inches is being ground in a lathe.
The surface speed of the bar is 29 ft/min. How many revolutions will the bar make in 51 sec?
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Let n be the number of revolutions per minute.

The diameter of the bar is d = 2*6 inches = 12 inches = 1 ft.


The surface speed of 29 ft/min is  the circumference  pi%2Ad times the number 
of revolution per minute, so we have this equation

    29 = 3.14%2A1%2An.


From this equation 

    n = 29%2F3.14159 = 9.231  revolutions per minute.


The number of revolution in 51 seconds is  %2851%2F60%29%2A9.231 = 7.846   (rounded).    ANSWER