Physics 151 Week 4 Day 1 Topics

– Strategic Problem Solving Strategy – Motion Diagrams & Motion Graphs with acceleration

Example: Velocity Vectors

Jake throws a ball at a 60 ° angle, measured from the horizontal. The ball is caught by Jim. Draw a motion diagram of the ball with velocity vectors.

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What to do to do well in this class

A. Focus on key physics concepts • May seem like basics but will help you solve even complex problems • Focus on principle rather than recipes • Need to have a functional understanding of key concepts • Express key equations as sentences • Know where they come from and what they mean • Know how and when to apply them • Know which equations are general and which are special cases • Must know when not to apply special cases • Look at a problem after a good physics diagram and maybe a good physical diagram and know what key physics concepts apply in that problem • Memorize key concepts so you can look at a problem, say that’s Newton 2, and know the associated equation in a snap Slide 21-16 Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

What to do to do well in this class

A. Focus on key physics concepts • How to do this • When you look at problems, mentally group problems by the physics rather than the physical situation • After each class or at least each week, create a notesheet to organize a structure of the new key concepts for each chapter and note how they fit in with previous key concepts • Use the note sheet to do homework problems (a) do as many homework problems as you can just using this sheet. (b) then go to your notes and the textbook for your missing pieces • Use flash cards to memorize key concepts - include the concept description, relevant equations, diagrams, and what types of problems benefit from using that concept • Pay close attention to examples done in class and note the physics and assume/observes in each example and how these are used Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

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Problem Solving Strategy (PSS)

When solving problems, it is important to show how you reasoned from the information given in the problem and key physics ideas to your final answer. The correct final answer with units is only worth 1-3 points. The remainder of the points (70-90% of credit) are awarded for the quality of your solution. You are expected to include the steps in red the following to receive full credit. The other steps are required on written solutions to homework problems but will be extra credit on exam problems.

Prepare •

Identify the Physics:

State explicitly which physics’ principle(s) apply to the problem situation and that you will use to solve the problem •

Drawing a Picture:

Draw at least one picture to visualize the physics of the problem and define your variables and constants. For motion problems this could be a motion diagram, motion graph, or pictorial diagram •

Collecting Necessary Information:

State all the information given in the problem with correct units.

Include preliminary calculations

such as unit conversions •


State assumptions or observations that would be useful Solve •

Start with key equation(s)

• in symbol form

Solve for the unknown quantity in symbols

Then substitute numbers with units

before numeric calculations and calculate the numeric answer Assess •

Check to see if your answer is reasonable

• Does it answer the question that was asked • Does it have the right units?

Solving Problems - Prepare (also identify key physics)

Solving Problems (continued)

Example Problem 2.14

In an 8.00 km race, one runner runs at a steady 11.2 km/hr and another runs at 14.2 km/hr.

How far from the finish line is the slower runner when the faster runner finishes the race?

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Motion Graph Demonstrations

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