Day 16: Too Hard or Just Right?

Tuesday, 6 September 2016

Today, I got a homework question from a student that I didn’t know how to answer right away. (Yeah, so this is the first time I’ve used a textbook’s questions for some of my homework problems, so it’s a new issue to me.)


The wave’s speed was given in the problem as 265 m/s.

Me: “Um, how are we gonna solve this?”

Student: [thinks to self: isn’t that what I just asked you?] “I don’t know. Maybe use d=vt?”

Me: “I’m not sure how to use it to help. Let’s set it up and see what we can learn.”

Both of us try a few things, get nowhere, and come back together.

Me: “We’re stuck, aren’t we? Why don’t we get a feel for it by drawing out a few more pictures?”


I realize the last two images might not progress quite right. Ugh, my sloppiness hurts to look at in this recreation of the drawing we made in class.

I asked my computer-science teacher colleague how he’d have gone about explaining the solution. We happened to be carpooling today, so yeah, that was convenient. Almost immediately he went to a geometric explanation, “they’ll meet back at a point that’s mirrored across the midpoint from the start point. One wave pulse travels a short leg then a long leg while the other travels a long leg then a short leg.” Dude, I see it! That Eliot, such a good generalizer. I swear it’s a gift of good programmers.

Was I the only one who couldn’t see the solution right off the bat? I took to Twitter to see how y’all would solve it. Y’all weighed in (side note: the amount of work friends on Twitter will put in on a shared question amazes me):

Bottom line? This is a super-cool question that only seems tough when you’re in equation-hunting mode. But with basic reasoning, it’s not too hard to figure out logically. That’s all I want my kids to see, so I’m glad it showed up in a WebAssign problem set this week.


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