Calvin Of The Jungle

Calculus Level 3

Last summer, I went zip lining through the Ozark Mountains. There are two platforms, and you can see the higher platform in the top left of the image, while the cameraman is standing on the lower platform. There is a rope tied between these two platforms, and I hanged from a pulley suspended on the cable. In this way, I was propelled by gravity towards the lower platform.

The horizontal distance between the platforms was 100 feet, and the vertical distance between the platforms was 15 feet. The rope joining the platforms was 102 feet long, and remained taut throughout my journey (rope from me to either platform was a straight line). As I swung through the jungle, what kind of curve did I trace out?

Arc of Catenary Arc of Ellipse Arc of Straight Line Arc of Parabola

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2 solutions

Faraz Masroor
Mar 21, 2014

Since the rope is taut throughout the sum of the distance between you and the first platform, and the distance between you and the second platform, adds up to the length of the rope, a constant. This is the definition of an ellipse.

But of course!

John King - 7 years, 2 months ago

Oops! But in the picture, the rope does not appear taut .... and is a catenary. However under the assumption that it is taut, the curve will be an ellipse.

Shabihe Baqri - 7 years, 2 months ago
Divyanshu Singal
Mar 22, 2014

Since the rope remained stretched throughout your journey, so we can consider the rope between you and the first platform and that between you and the second platform, straight lines. The sum of distances between you (the locus point) and the two platforms (foci) remain a constant (the length of the rope). So you trace out an ellipse, by definition.

not vertices , but focii.

debasis bhattacharya - 7 years, 2 months ago

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Yes. you are right. it should be foci. so i have edited my solution

Divyanshu Singal - 7 years, 2 months ago

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