Designing a buoy teather

Binkai · Sep 17, 2012

Consider a buoy in the form of a vertical right circular cylinder of outside diameter (D) of 8 feet, and
height (H) of 12 feet. The buoy is a hollow cylinder formed of glass-fiber-reinforced plastic (FRP)
that is ½-inch thick. The buoy is to be placed in a large river and tethered to the bottom by a cable
that is 80 feet long. The cable is supposed to snap if the water depth exceeds 90 feet. Compute the force on the cable at different river depths and the force at which
the cable should be designed to snap. Create a graph of cable force as a function of river depth. I'm totally lost. No idea where to begin.

harrylin · Sep 18, 2012

Binkai said: ↑

Consider a buoy in the form of a vertical right circular cylinder of outside diameter (D) of 8 feet, and
height (H) of 12 feet. The buoy is a hollow cylinder formed of glass-fiber-reinforced plastic (FRP)
that is ½-inch thick. The buoy is to be placed in a large river and tethered to the bottom by a cable
that is 80 feet long. The cable is supposed to snap if the water depth exceeds 90 feet. Compute the force on the cable at different river depths and the force at which
the cable should be designed to snap. Create a graph of cable force as a function of river depth. I'm totally lost. No idea where to begin.

Hi welcome to physicsforums.
However, isn't that a homework question? Please look under Thread / Thread Starter of:
https://www.physicsforums.com/forumdisplay.php?f=61

Homework questions go here:
https://www.physicsforums.com/forumdisplay.php?f=152

Pkruse · Sep 18, 2012

I remember getting this same question in 9th grade in 1971, but it was a steel buoy. I answered it "not enough information." I went on to explain that I needed the river current. This would obviously be at flood stage, where the component of line tension caused by the current may dominate over buoyant forces. The teacher gave me full credit.

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