Become Proficient in School Physics Problems

[Isaac0427]

I'm not sure if this is the right forum, but I wasn't sure where to post this.

I was just wondering how long a basic high school physics problem should take you for you to be considered proficient. Specifically, projectile motion problems and force/tension problems that require you to look at the x- and y-components of the force vectors. For example, a problem modeled by this picture (on the left)

where you are given 3 pieces of information and you have to find the fourth (either vi, d, h or theta) and the final velocity of the water. Or a problem like this

where you are given the angles and the mass of the bag.

Thanks!

 

[PeroK]

Although many people find it useful to do several problems that are much the same, I would say that proficiency involves seeing the general solution and realising that if you change the numbers it's really just the same problem again. And, being able to sanity-check the solution - what happens as $\theta \rightarrow 0$, does my solution make sense?

Perhaps at high school level it is useful and important to get the methods engrained by repetition, but if you take a mechanics book like Kleppner and Kolenkow, the problems are almost entirely algebraic.

Personally, I don't think it matters how quickly someone can plug and chug (!), but rather how well they understand the physical and mathematical structure of the solution.

 

[Dr. Courtney]

In the first year Physics courses I have taught, most exams required students to work 4 problems of that level of difficulty in 50 minutes - an average of 12.5 minutes each. Most students would finish a couple problems quickly that they remembered how to do right away and use the balance of the time on the ones they found harder.

 

[Isaac0427]

Thanks! As professionals, when you see a problem like this, do you just look at it and immediately know what to do and what equations to use? How long does it usually take you?

 

[Student100]

Thanks! As professionals, when you see a problem like this, do you just look at it and immediately know what to do and what equations to use? How long does it usually take you?

In the spirit of the question there's only one equation you need here F=ma. Everything else can be obtain directly from it. So yes?

I don't think it's right to say we could look at it and instantly know how to "solve it." Without context I might look at the picture and develop a different set of assumptions. With the context that was provided it's trival to develop a general solution. So yes?

I wouldn't get caught up on how long it takes you. Obviously it's important for exams and tests, but the initial goal should be understanding. You can be proficient without speed. Speed comes with lots of practice and experience.

Instead to become proficient make sure you understand why you approach a problem a certain way, what the equations tell you, do they make sense, do extreme cases provide any interesting insights, etc.

 

[Logical Dog]

when i was in my prime for a level mechanics I could solve those under 3-10 minutes. Looking back since I have forgotten a lot of the basics, It would take me anything from 20 to an hour Most of it would be spent remembering the approach and the basic assumptions. They are looking like pretty simple problems to me especially the cement bag one with it being in equilibrium and all...shouldnt take long. Its not about being quick, but being able to know which models fit with the situation and use correct equations, i guess.

One of my best memories was in an exam where we had a question about a box attached to a mass on a pulley hanging from a table, the mass is released and the rope breaks after some time, then we were asked to find if the box falls off the table and how far it travels or something like that. It was really fun, mechanics can be quite fun to get right. I got very excited and wrote a lot of english and physics on it and the teacher wrote a remark "good" on the side, i don't remember the specifics but it was a question of a higher complexity than the norm, we had to apply knowledge and not plug and chug

This is the official exam that I gave:
https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9709_s14_qp_42.pdf

its out of 50, I got 40. The time is one hour 15 minutes. You should start going for maths and physics olympiads because you are young and ambitious. There you will be exposed to questions in a different manner and level than just from regular university and school courses, so if you want to develop proficiency in physics and maths, that is my recommendation. Even a dumbo like me can pass exams well given training, time and lots of practice.