In 2014, an exam question regarding a hypothetical helicopter and rope scenario went viral for the usual reason: almost no one could agree on the answer. Always in the pursuit of knowledge, educational science YouTuber Derek Muller, who runs the channel Veritasium, recently set out to provide the undisputed answer to that question.
And how do you find the definitive answer to such a question, you might ask? If you run a famous YouTube channel with lucrative sponsorship deals, the best way is to simply rent a helicopter and turn the hypothetical scenario into a real one.
Finding the answer to a viral exam question
In a video (embedded below), which is currently sitting at just over two million views, Muller reads out the scenario outlined in the 2014 qualifying exam for the U.S. Physics Team: "A helicopter is flying horizontally at a constant speed. A perfectly flexible uniform cable is suspended beneath the helicopter. Air friction on the cable is not negligible. Which of the following diagrams best shows the shape of the cable as the helicopter flies through the air to the right?"
Here are the answer choices that had science enthusiasts and experts in such disagreement:
What do you think the answer is? Before running his experiment, Muller ran a poll on his channel in which the highest scoring answer was C, followed by B. No one thought E was the correct answer. We can provide a hint from the exam paper itself, which is now posted on the American Association of Physics Teachers' (AAPT) website. In the solutions section following the question, the paper explains that "since there is air friction on the cable, then there must be a horizontal component to the force where the cable attaches to the helicopter."
A question that 'generated a great deal of controversy'
Still not sure? Well, as Muller points out in his video, which states the answer, there are two external forces acting on the rope: gravity, which pulls it downwards, and air resistance, moving it to the left. "When flying along at constant speeds, these forces must be perfectly balanced by the tension in the rope," Muller says. In his video, Muller uses a battle rope like the ones used in gyms. He also runs the same test with a 20 lb (9 kg) kettlebell and then a parachute attached to the rope — because if you get to rent a helicopter to run a science experiment, you're going to make the most of it.
It's worth checking out Muller's video, if only to witness the sheer audacity of someone renting a helicopter just to settle the score on a disputed viral exam question. On the AAPT exam paper, under the solution, the exam writer states that "this question generated a great deal of controversy" and that "at least two test-takers challenged the answer." Surely now, they can't have anything to argue about?