Physics Problem: What Value Would This Scale Read?
This problem has been around for quite a while — and it’s usually very popular. It goes like this:
Suppose you have two 200 gram masses hanging vertically by a string. The strings for both masses go over a pulley and connect to a single scale that measures the force in “grams” — just to make the problem easier. The question: what value does the scale read?
Oh, wait! I’ll make this multiple choice for you.
- 200 grams
- 400 grams
- 0 grams
- something else
While you are thinking, let me give some comments about why this is such a fun question. First, it’s a question that pretty much everyone has an answer for. It’s not one of those questions where people will just say “oh, I have no idea”. Everyone has an idea. Second, for three of the multiple-choice answers above I think you could produce a plausible reason for why that answer makes sense. That’s actually important. Even if an answer is wrong, it has to make some type of sense.
Now for the answer. Well, I’m going to start off with the explanation of the answer. Let’s think about the scale. I’m going to actually set up this experiment using a digital scale–but it could be any type of scale. Suppose it’s a spring scale. These scales measure…
