A Sunday Morning Brain Teaser For You

Hey, I know just you want on a Sunday morning! A physics problem! If it helps, think of it as a brain teaser. Like many such, it's deceptively simple, but when you start to think about it a lot of concepts collide and it's not as obvious as you might suppose at first glance. Here's my friend Dianna Cowern, aka Physics Girl, with the brain-stumper. I suggest you do as she recommends, and stop the video to think about it before she gives the answer. Did you get it right? I will admit it: I did. Fo...