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Propeller and Circumference Quest

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by preciousrain7 » Tue Feb 19, 2008 5:04 pm
The end of a blade on an airplane propeller is 10 feet from the center. If the propeller spins at the rate of 1,320 revolutions per second, how many miles will the tip of the blade travel in one minute? (1 mile = 5,280 feet)

1. 200π
2. 240π
3. 300π
4. 480π
5. 1,200π

If anyone can explain to how tackle this problem I'd really appreciate it. Didn't understand the original explanation. Thanks in advance

The official ans is: C
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Answer

by keerthivivek » Tue Feb 19, 2008 7:50 pm
The tip of the blade covers a distance equal to circumference of the circle for one revolution. The circumference = 2 * pi * 10

How many revolutions does the point complete in 60 seconds ( 1 min ) :
1320 * 60.

Total distance covered for 1320 * 60 revolutions in feet
= 2*pi * 10 * 1320 * 10.

Converting this distance to miles using the expression in the question takes us to 300 * pi
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by its_me07 » Wed Feb 20, 2008 2:16 am
The formula is
No. of revolutions=distance/circumfrence


Hope this helps.

Paresa
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by abhi75 » Wed Feb 27, 2008 10:20 am
Hi Keerthivivek,

Thanks for the explanation but you have a typo.

Total distance covered is not = 2*pi * 10 * 1320 * 10.
but 2*pi * 10 * 1320 * 60.

Conversion will be 2* pi *10 * 1320 * 60/5280

Answer is 300pi

-A
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