Help Solve Physics Problems - Physics Forums

[Diane_]

https://www.physicsforums.com/showthread.php?t=95887

1) If anyone has any ideas to help this kid, you might consider posting them. I know we're not supposed to give "complete solutions", but:

2) I truly despise things like this, where a grade depends not so much on your understanding of the material but on spotting some trick. I will do things of that nature as extra credit questions, but I make it a point never to put trick questions as main questions on tests or quizzes.

I'm just wondering if I'm overreacting to this or if others agree with me.

 

[Pengwuino]

Yah that's definiitely one of those "spot the trick" crap problems. The teacher probably thought up some nifty little trick and wondered how many people would be able to figure out his lil trick to doing it.

I can't figure out what you would do. Gravity works in the vertical direction and it soudns like the guy is stuck with a horizontal propulsion problem.

 

[cronxeh]

It would help if he posted the problem originally worded and not tried to describe it in his own words

 

[moose]

https://www.physicsforums.com/showthread.php?t=95887

2) I truly despise things like this, where a grade depends not so much on your understanding of the material but on spotting some trick. I will do things of that nature as extra credit questions, but I make it a point never to put trick questions as main questions on tests or quizzes.

Well, what is it that someone does in a real job? Exactly.

These projects though, almost always have to do with what you just studied that week.

 

[Diane_]

Well, what is it that someone does in a real job? Exactly.

If you're talking about creative problem solving, then yes, the soi disant real world does abound with those. However, the universe doesn't as a rule go out of its way to make you look one way while something interesting is going on in the opposite direction. Subtil ist der Herr Gott, aber boshaft ist Er nicht, to quote someone I admire.

These projects though, almost always have to do with what you just studied that week.

Yeah - if you read the thread, you know I asked him about that. About all he could say is "we were studying Newton's Laws" (which makes sense) and "it has something to do with gravity" (which doesn't).

 

[Moonbear]

It's hard to know if the kid is explaining it accurately or not. My first thought was not to have a wire parallel to the ground, but that was added later by the student. So, is that their own "inside the box" thinking of how it will be set up, or part of the actual instructions? It may not be a trick at all, and gravity may play part in it if we aren't being given the proper instructions. I can think of several other creative solutions, but don't know if the students are limited to only one balloon...since they are given 5, but the student states get "a" balloon across and back, well, which one is the actual assignment? Can the balloon that goes across and back have helper balloons? I think this is one that the students need to work out for themselves to learn to be creative thinkers.

 

[Diane_]

So maybe I'm overreacting. It still doesn't feel like that.

I do give my students assignments that require them to apply what they're learning. One of my favorites - we were discussing momentum and impulse, and they were required to design an apparatus that would allow them to run full speed into a wall and not be hurt. "Full speed" was defined as "airborne for the last meter." They were also told that no two designs could be the same, first come, first served. To make sure they wouldn't be hurt (and I wouldn't be sued), they were required to submit their design before proceding including an explanation of how it was supposed to work.

The results were great. The first team used the obvious "loads of pillows against the wall." The second team, with their idea stolen, modified it to "loads of pillows on the runner". After that, things got creative. Bungee cords, break-away barriers, and others I no longer remember. On the day of the lab, we had three other classes show up to observe. Each team explained the physics behind their apparatus, then demonstrated. One class set themselves up as judges a la the Olympics, awarding points for style and artistic interpretation.

The thing is, that particular assignment did not depend on finding one and only one solution. If I want to give an assignment like that and can't think of at least two ways to do it, both outgrowths of class discussions, then I either modify it or abandon it. Perhaps I'm wrong, but this one seems like the teacher thought up one clever way to solve the problem and then set it up so that no other solution could be used.

It's possible that the student isn't transmitting the instructions correctly, and (as I said) it's possible I'm just overreacting to a style I think inherently unfair, but assuming things are as indicated, I still feel there's something wrong with this.

But I'll shut up now. :)

 

[Moonbear]

The thing is, that particular assignment did not depend on finding one and only one solution. If I want to give an assignment like that and can't think of at least two ways to do it, both outgrowths of class discussions, then I either modify it or abandon it. Perhaps I'm wrong, but this one seems like the teacher thought up one clever way to solve the problem and then set it up so that no other solution could be used.

I can think of more than one solution that does not require the guide wire be on an incline (though that was the obvious first approach until that was ruled out...it's the only approach that really fits with the "gravity" comment, but not the only approach that should work). Russ suggested one method, I can think of a few variations on that theme, as well as an interesting use for paperclips other than as clips. But, since I think the intent is creative thinking, I'm not going to suggest them all to the student.

It also may be that the teacher has only one clever idea in mind for solving the problem, but it doesn't rule out whether they will be graded for their approach to solving the problem rather than whether they found the one solution. I don't see that as the same thing as a trick question. Many problems and class assignments only have one solution. A trick question is more when you are given deliberately misleading information, such as a multiple choice question where the right answer is not one of the choices and you're supposed to somehow know to write in the correct answer.

The only thing I hope is that the instructions were written for this assignment. If only given orally, it leaves too much room for misinterpretation and you can't go back to double check them as you could for written instructions, such as to go back and see if it really says the guide wire must be parallel to the ground.

 

[Danger]

Well nuts!
I just saw this now, and it's too late to help. There are a few different ways to (maybe) accomplish it, depending upon some physical properties of the guide wire.

 

[Diane_]

I can think of more than one solution that does not require the guide wire be on an incline (though that was the obvious first approach until that was ruled out...it's the only approach that really fits with the "gravity" comment, but not the only approach that should work). Russ suggested one method, I can think of a few variations on that theme, as well as an interesting use for paperclips other than as clips. But, since I think the intent is creative thinking, I'm not going to suggest them all to the student.

Inclining the wire was the first thing I thought of, too. I'm curious what your other ideas were - I'm tolerably certain that the student will never see them if you post them here. As I recall, the assignment was due some time ago anyway.

It also may be that the teacher has only one clever idea in mind for solving the problem, but it doesn't rule out whether they will be graded for their approach to solving the problem rather than whether they found the one solution. I don't see that as the same thing as a trick question. Many problems and class assignments only have one solution. A trick question is more when you are given deliberately misleading information, such as a multiple choice question where the right answer is not one of the choices and you're supposed to somehow know to write in the correct answer.

Well, I certainly can't argue with any of this, particularly your definition of a trick question. I just wish I knew what he had in mind.

For what it's worth, I generally don't do multiple-guess questions on tests. Answers to things like that tell me nothing useful about the student's understanding of the processes. Occasionally, a class will prevail upon me to give them a multiple-choice test, but no class has ever asked more than once. On all of my muiltiple-choice questions, I include (e) None of the above - supply your own answer. Thus I refute multiple-choice.