<p>Slightly unrelated - the physics behind this gif is absolutely amazing!
<a href=“http://d24w6bsrhbeh9d.■■■■■■■■■■■■■■/photo/aM1v5xx_460sa.gif”>http://d24w6bsrhbeh9d.■■■■■■■■■■■■■■/photo/aM1v5xx_460sa.gif</a></p>
<p>An old, experienced physicist from PhysicsForums.org has confirmed the straight slanted line. </p>
<p>Someone should actually do an experiment and tell us the results haha…maybe that would be simpler</p>
<p>@greenbat23, @majorineverythin - BTW I answered slanted line on the test too, but think it’s wrong. Here’s my counter argument to your solutions:</p>
<p>Let us consider a though experiment… Imagine that the helicopter is going really, really fast. Then the string is horizontal. Then the helicopter slows down a little bit, the question is, does the tip of the string sag before the portion before the tip? The answer is yes. That is because all section of the string has tension before and just after holding it up. The very tip at the end does not have tension holding it up, so it will start sagging down. The higher up the string to the helicopter, the greater the tension of the rope because of more mass underneath. You essentially have a length-dependent tension on the string, which will yield a downward-concave profile, since a linear drop in tension (which is force), will result in a non-linear profile.</p>
<p>Anyways, I gotta run off to study for my AP Chem exam for this Thurs, AP Physics E&M on Fri, and Stochastic Process on Fri as well. Need to review all my Markov Chain stuff. I’ve wasted so much time studying for the AMC 10A and then 12B that I’ve been neglecting my school a bit. Need to catch up.</p>
<p>@tigerbookmark, what was your original thought process that lead you to choose the straight slanted cable?</p>
<p>My apologies, but the universe has spoken in favor of me: <a href=“http://oi60.■■■■■■■.com/v6q694.jpg”>http://oi60.■■■■■■■.com/v6q694.jpg</a></p>
<p>Also, @tigerbookmark, this argument has been made many times here. Unfortunately, it is wrong. It is true that the tension increases as you go up the rope. However for any small mass element of the rope, there is a tension force that acts upward AND downward. They cancel out to become the same magnitude upwards for every mass element.</p>
<p>@tigerbookmark</p>
<p>it’s actually nearly impossible to be horizontal - the force making it horizontal is the drag force, which reduces to 0 linearly as the angle to the horizontal decreases. unless, of course, you’re accelerating to the right.</p>
<p>furthermore your assertion of what happens when you’re decelerating doesn’t matter because we’re talking about steady-state (equilibrium) position. obviously, our solution doesn’t work when the rope/helicopter is accelerating.</p>
<p>If the official answer key has been released on Friday, can we view it online anywhere?</p>
<p>No, it has not been released yet.</p>
<p>@tigerbookmark I believe that you mean the string tends to want to stay straight and thus the end of the string will drop first. “That is because all section of the string has tension before and just after holding it up” The F=ma test said perfectly flexible so the only tension possible is parallel to the string. Anything that is slightly off to the side would require a stiff rope. </p>
<p>@torusdonut Here is my solution: A string from the helicopter can be replaced with any material with the same dimension, as the same forces act upon the object. The only restraint is that the object is the same size and width. Therefore, assume that the string becomes a steel rod. The steel rod is obviously straight, so it has to be straight.</p>
<p>2014 USAPhO result is out!</p>
<p>total 431 semifinalists.</p>
<p>CA: 168 students</p>
<p>@xiaorui Where are they posted ? And what’s the cutoff?</p>
<p>woah wait what where is this I’ve scoured the entire AAPT website and nothing</p>
<p>I don’t know the cutoff yet. Search the pdf file!</p>
<p>what pdf file @xiaorui ?</p>
<p>same lol i can’t find it.</p>
<p>can you link to it?</p>