document.write( "Question 666771: Each tire of an automobile has a radius of 1.25 feet. How many revolutions per minute does a tire make when the automobile is traveling at a speed of 65 feet/sec? \n" ); document.write( "
Algebra.Com's Answer #414691 by DrBeeee(684)\"\" \"About 
You can put this solution on YOUR website!
This is too neat of a problem to pass up, so here goes! I hope I can explain the solution well enough for you.
\n" ); document.write( "First we want to calculate how far we travel with each revolution of the tire. It is the circumference of the tire. Agree?
\n" ); document.write( "Using
\n" ); document.write( "(1) Circumference = pi*d, where d is the diameter of the tire or 2.5 ft., we get
\n" ); document.write( "(2) Tire rotational distance per revolution = 2.5*pi ft/rev.
\n" ); document.write( "Now how fast is the car moving? It says 65 ft/sec which is
\n" ); document.write( "(3) Car Speed = 65 ft/sec or
\n" ); document.write( "(4) Car Speed = 60*65 ft/min or
\n" ); document.write( "(5) Car Speed = 3900 ft/min
\n" ); document.write( "Now we want the third/final calculation that gives us the tire rotational speed in revolutions per minute. This is given by
\n" ); document.write( "(6) Rotational Speed = (ft/min)/(ft/rev) or using (5) and (2) we get
\n" ); document.write( "(7) Rotational Speed = (3900 ft/min)/(2.5*pi ft/rev) or
\n" ); document.write( "(8) Rotational Speed = 1560/pi rev/min or
\n" ); document.write( "(9) Rotational Speed ~ 497 rev/min
\n" ); document.write( "Answer: The tire is rotating at the rate of approximately 497 revolutions per minute.
\n" ); document.write( "Note my use of what is called dimensional analysis to keep our calculations straight. For example, look at (6) where we have (ft/min)/(ft/rev) which, when evaluated is (ft/min)*(rev/ft) = rev/min, because ft cancels. \n" ); document.write( "
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