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This text is meant to accompany class discussions. It is not everything there is to know about uniform circular motion. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

Click for the questions that go with this reading
Strategy for solving word problems
  1. Draw a picture labeling any numbers thta appear in the problem. (I don't always require this step but it can be very helpful.)
  2. Identify the givens by looking for unit clues, key words and phrases like drop, rest, and "constat velocity."
  3. List these givens with the variable, number, and units. Include the variable you are looking for in your list.
  4. There are 4 kinematics equations. Find the formula that contains all of /only the variables and unknown.
  5. Plug in numbers and units then solve.

 

"Race Style" problems

 

"Race style" problems are where two bodies race side by side. In its most basic form, the two bodies cover the same distance in the same amount of time. Below is a video describing how to solve this type of problem and what we re looking for to give you credit to communicating your solution.

 

 

 

Highlights

  • Each car has an acceleration and an intitial velocity.
  • You will always make two lists of givens. One for each body. For organization and comunication reasons make the two lists side-by-side.
  • The lists will always have a acceleration and an intial velocity.
  • When solving, you will always use x = xo + vot + (1/2)at2
Example #1
  • Question
  • Hint
  • Solution
  • Video Solution
Two runners are at track practice. Randal is tunning at a constant speed of 9.3 m/s. Race is ahead of Randal and running at 6.1 m/s. Randal is approaching Race to pass him. At the instant Randal is next to Race, Race begins to speed up at 0.77 m/s2. How much time is needed for Race to catch up to Randal?
  • The question is talking about the runners starting side-by-side and ending up side-by-side. Therefore they cover the same distance in the same amount of time.
  • There two accelerations so you will need two lists of givens.

This HD video is on YouTube at http://youtu.be/S_Qtc7Hc_1I

 

 

Example #2
  • Question
  • Solution
  • Video Solution

Setup Picture

A police car stopped at a traffic signal. A red sports car passes him while accelerating at a constant 0.500 m/s2 and traveling at 8 m/s when he was 11.0 m away. The policeman takes a moment to think about what is happening and begins to accelerate at 3.50 m/s2. How much distance will it take to catch the red sports car?

Solution

 

 

 

"Segmented" Problems (Multiple Accelerations)

These are problems with multiple accelerations for one moving body. The video below describes how these can be solved.

 

 

 

The main point to remember is that each acceleration gets it own list of givens. It the "race" style problem 2 cars with 2 accelerations get two lists of givens. In the segmented problems, again, multiple accelerations, for one body, also means multple lists of givens. One list for each acceleration. This concept will be built upon later in projectile motion.

 

 

Example of a "Segmented" Kinematics Problem
  • Question
  • Hint
  • Solution
  • Video Solution
A car is traveling at 5.0 m/s when it speeds up at 3.0 m/s2 for 4.0 seconds. The car then travels at a constant velocity for 100.0 m. After which time it slows down with a deceleration of 2.00 m/s2 for 15 m. What is the car’s velocity at the end of the trip?

A car is traveling at 5.0 m/s when it speeds up at 3.0 m/s2 for 4.0 seconds. The car then travels at a constant velocity for 100.0 m. After which time it slows down with a deceleration of 2.00 m/s2 for 15 m. What is the car’s velocity at the end of the trip?

HINT:

  • The vehicle undergoes multiple accelerations.
  • Each acceleration gets its own list of givens.
  • The final velocity for one segemnt becomes the initial velocity of the following segment.

This YouTube video is located at http://youtu.be/TCIwwZi5qUU

 

 

quiz 4
Choose the best answer. It does not matter how many questions you miss. What matters is that you learn from any mistakes.

 

 

 

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by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)