# USAPhO 2014 F=ma exam #19, (tension, static equilibrium)

**1. The problem statement, all variables and given/known data**

A choppah is flying horizontally at constant speed. A perfectly flexible uniform cable is suspended beneath the choppah; air friction on the cable is NOT negligible.

Which of the following diagrams best shows the shape of the cable as the choppah flies through the air to the right?

I’ll try to help you visualize the cable shapes depicted in the problem:

1) the cable is straight and vertical

2) the cable is straight and slanted, like a y = x graph

3) the cable is curved, like a y=x^2 curve, Q1 (but not exactly)

4) the cable is curved the opposite way, like y = √x , Q1, (but not exactly, you get the idea)

5) the cable looks like y = x^3 , Q1 & Q3, (not exactly though, more squashed into the y-axis)

**2. Relevant equations**

This is a visualization problem, I believe. Handy to remember that the force of gravity, the tension at each point, and the force of air resistance each play a role.

**3. The attempt at a solution**

I put 3 as the answer. I thought that is the mass was negligible, it would be 2, a straight slanted line. However, gravity acts at the center of mass, pulling down the slant in the middle.

Now I realized I hadn’t taken air resistance into account.

Your solution? Thanks.

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