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Journal for Practical Physics Education, 2019 > How to solve a physics problem


25 Apr 2019

A lot of students have difficult time when facing the task of solving a physics problem. Questions like where do I start from, what to do, etc. storm their minds. In this short presentation I would like to give some guidelines on how to approach any physics problem.

First of all I would like to stress that any physics problem consists of two parts. I would call them the physics part and the math part.

In the physics part which is where any problem starts from we have three main steps;

a) A table which should include what are the given of the problem and what it ask us to find. This will help the student to find which topic/s of the course the problem refers to. This is particularly important on final exams where one is tested in the material covered over the whole year or semester.

b) A diagram which includes a free body diagram if applies. It is very important to help the student visualize the situation that the problem refers to. As the great of all times Albert Einstein famously said "Imagination is more important than knowledge. For knowledge is limited to all we know and understand, while imagination embraces the whole world, and all there ever will be to know and understand". Visualization is a step between imagination and reality and in this case will help the student to understand the given problem better.

c) Write down the formulas required to solve the problem. Here the student can use step (a) to figure out which formulas are related start writing all of them down and keep the ones that really are required for the solution of the problem.

And now we go to the second part which is the math part of the solving process. Again here we have three steps;

a) Once the student picked the formulas required for the solution of the problem he/she should have a system of equations to solve. One indication that the student is in the right direction the student should have the same number of equations as unknowns, because otherwise the system will not have a solution. Depending on the mathematical level of the student, can either use one of the algebraic methods of solving a system of equations (substitution, comparison,elimination) or by using the augmented matrix using Linear Algebra.

b) Solve the system symbolically. By symbolically I mean using the symbols that represent the physical quantities (F for force, m for mass, etc.) and keep the numerical values if given for the end of the problem.

c) Finally, work out the units of the problem. Besides being an important part of the solution of the problem for which most if not all of the teachers will take off marks, if you skip it, it will help the student to check if the solution is correct. If the units of the final solution match the dimensions of the answer it means that most probably the solution is correct, otherwise it is an indication that something went wrong. For example if the problem asks to find the force of friction and the student finds as an answer 15kg for sure something is not correct.

George Lerakis, Montreal Math & Physics Tutoring

 

 

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