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kelcharge

Think your smart, I thought I was...

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Quote:
Original post by kelcharge
Two people got it right. It was 137 degree's, but at least I know I'm not the only one. No offense jjd. :)


You're kidding aren't you? jjd got it absolutely right, the chain doesn't start wrapping around the cylinder until it hits 90 degrees. Where did you get the question from?

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It first takes 90 degrees until the chain catches and begins to wrap around the cylinder. As jjd explained, that leaves 7 inches left. The formula for arc length is:

s = n * pi * r / 180

And solving for n we have

7 = n * pi * 5 / 180
n = 80.3 degrees

Adding that to 90 leads us to 170.2 deg.

Ergo, what jjd said.

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Quote:
Original post by kelcharge
Two people got it right. It was 137 degree's, but at least I know I'm not the only one. No offense jjd. :)


haha! no way! [wink] Those answers assume that the chain sticks to the cylinder all the way. But since the chain starts at the bottom, that can't be the case until the cylinder rotates through 90 degrees. If I were to use that rationale, I could raise the bar by 5 inches by only rotating the cylinder through 57.2 degrees [smile]


-Josh



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Quote:
Original post by skittleo
I think kelcharge's logic would work if the chain had no length...


Ooh! I like that [smile]


-Josh

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The way the math works out. This would be be correct if the metal bar was hanging in a hole or something that keep it from moving horizontally.


The way physics and jjd would work it out. The chain won't touch the cylinder until after the cylinder was rotated more than 90 degrees.

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Quote:
Original post by skittleo
I think kelcharge's logic would work if the chain had no length...


...and if we knew how long the bar was
...and how far from the ground it started

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The question is not explicitely clear. We assume that the bar sits on the ground at the start of the rotation. This is not specificied. So it is possible the bar is already one foot off the ground and no rotation is necessary. This question is moot.

Edit:

Quote:
Original post by Neil Kerkin
Quote:
Original post by skittleo
I think kelcharge's logic would work if the chain had no length...


...and if we knew how long the bar was
...and how far from the ground it started


Too fast for me. =P

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Quote:
Original post by skittleo
The question is not explicitely clear. This question is moot.


Agreed. Kelcharge, you really should talk to your teacher about the ambigouity of this problem if by chance you answered the 170.2° Now unless a diagram was provided, I think you can have a valid argument.

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