## Introduction

My high school physics teacher stole this from one of his professors. To this day, I recall him saying, “I’m sure one of you will steal this from me.” I vowed to be the student that stole it from him. They used to be Paquet’s Laws[1]. I’ve made some updates and slapped my own name on them. My students have always found them useful. I hope you will too!

## How to Solve Any Physics Problem

Honestly, this works for pretty much every physics problem. I got through graduate course work using this approach.

- Read the problem. I mean really dig in and
**read**it. - Record all given information,
**including**units… Units!! Units!! - Draw a picture representing the physics.
- Identify what the problem is asking for
- Link what you have to what you need. This is usually an equation.
- Put your information into the link
- Plug and Chugalug
- Inspect your answer. Does it make sense? Do your units work out?
- If 8 checks out you’re finished. If it doesn’t, go back to 1.

### How to solve a Vector Addition Problem

Vector addition problems are a sub-set of physics problems. Most everything we deal with (forces, angular momentum, etc) are vectors. Understanding how to break them up and combine them will be critical.

- Make an array of all vectors listing the vector, magnitude, and angle.
- Using trigonometry, find all of the x and y components of each vector.
- Calculate: $x_r = \Sigma x$ and $y_r = \Sigma y$. This gives you the x and y components of the resultant vector.
- Use $c = \sqrt{x_r^2 + y_r^2}$ to find the magnitude of the resultant vector.
- Use $\theta = arctan(y_r/x_r)$ to find the angle of the resultant vector.

### Important notes:

- All angles are measured from the +x-axis as being zero degrees.
- Since there are two tangents that have the exact same value, inspect your final direction. Ensure that you have it

going the correct way.

## Creating Study Guides

When studying physics you need a study guide. They keep you organized while codifying new information. A good study guide gives you a high level idea of what’s in the chapter. It provides a list of important equations and definitions. Writing out concepts in your own words ensures you understand them.

- Record the title of the Chapter
- Record the section heading
- While reading the section, record any bold face terms and equations. Don’t forget the meanings of variables!
- Note anything that confused you. Look it up in a different book, or speak with your professor to clear up these issues.
- Continue to repeat this process until you reach the end of the chapter.
- When you are finished make a crib sheet of all the important equations. Use the crib sheet to work on your homework.

- [1]J. Paquet, Paquet’s Laws, Private Communication. (2002).

## One Reply on “Stosh’s Laws”

The assumption that V(xf), V(yf) is incorrect. Clearly, as the projectile descends, it gains momentum. Based on the presentation, have the initial and final Y velocities set to zero implies no change in momentum. We know this to be false. If one does the problem as a vector problem, one will find that indeed the final Y velocity is -19.8 m/s. However, the Y motion is not linked to the X motion. Only by the convenience of the 45 degree angle, does this give the initial velocity in X the same value with the opposite sign. Actually, the final velocity is 28 m/s. Indeed, demonstrating that the momentum MV has increased due to the work done by the gravitational force! Remember, that the initial X velocity is conserved as is the momentum in X. Not so for Y hence the increase in velocity. As stated, the problem violates conservation of momentum…..