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Problem involving circles and distance travelled

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cssears
 Post subject: Problem involving circles and distance travelled
 Post Posted: Wed Mar 03, 2010 12:55 pm 
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Course Students


Posts: 15
I have run into several types of the these problems involving one of the measurements of a circle, a speed data point, and the question of distance travelled? Can you please walk me through the preferred MGMAT process to solve a problem like this?

Here is a an example:

A point on the blade of a windmill that is rotating in a plane is 10 feet from the center of the windmill (blade). What distance is travelled, in feet, by this point in 15 seconds when the windmill runs at the rate of 300 revolutions per minute?

Thanks,

Casey
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abhisec
 Post subject: Re: Problem involving circles and distance travelled
 Post Posted: Wed Mar 03, 2010 10:54 pm 
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Posts: 5
I think the easiest is to calculate the number of revolutions.

300/minute is 300/60 per sec = 5 per sec

in 15 secs 5 * 15 = 75 revs.

Now one revolution will make the point travel the circumference of the circle = 2 * pi *r

so 75 revs = 75 * 2 * Pi * 10 as r is given as 10 feet.
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cssears
 Post subject: Re: Problem involving circles and distance travelled
 Post Posted: Thu Mar 04, 2010 9:40 am 
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Course Students


Posts: 15
Thanks for the help, in summary the process is.

1. calculate the revoloutions that occur
2. calculate the circumfrence (feet travelled in one revolution in this case)
3. multiply together to get total distance traveled
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esledge
 Post subject: Re: Problem involving circles and distance travelled
 Post Posted: Sun Apr 25, 2010 11:10 pm 
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ManhattanGMAT Staff


Posts: 903
Location: St. Louis, MO
Exactly. You've noted the three components of such problems:

Linear distance travelled is a function of revolutions/sec and time (or # of revolutions, if given directly) and radius at the point in question.

The important thing is to remember how the three relate, not to memorize a prefered order. The order could change, depending on what is given. For example, a different problem might give linear distance travelled and # of revolutions, then ask for the radius.

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Emily Sledge
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ManhattanGMAT
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