CHAPTER 4 NOTES

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CHAPTER 4 NOTES Problem solving
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Steps to problems solving

1. Identify the unknown.
2. Identify what is known or given.
3. Plan a solution.
4. Do the calculations.
5. Finish up Check your work.

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Conversion Factors

• Equivalent measurements (equalities) can be used
  to create conversion factors. (1 m100 cm, 1.6
  km1 mi)
• Two conversion factors can be written from any
  equality.
• 2.54 cm 1 in can be written as two different
  conversion factors
• 2.54 cm or 1 inch
• 1 inch 2.54 cm

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Unit Conversions Example

• Convert 750 nm to km
• Unknown km
• Equalities 1 m 109nm
• 1000 m 1 km
• Solution 750 nm 1 m 1 km
• 1 109 nm 1000 m
• Solve 7.50 ? 10-10 km

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The most common mistakes can be avoided if you

• Dont take shortcuts!! Shortcuts equal errors!
• Write down all units. No naked numbers!
• Keep your work organized.
• Do a sensibility check. Make sure your answer
  makes sense.
• It must be human error to put the big number in
  the numerator. It doesnt always go there. Be
  careful!
• It is helpful to put in units first then put in
  numbers.
• Double check everything.

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Reasons for not using Dimensional Analysis

• Let's say you're super-intelligent and enjoy
  solving relatively simple problems in the most
  complex manner.
• Let's say you're tired of always getting the
  correct answers.

1.
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Reasons for not using Dimensional Analysis

• Let's say you're an arty type and you can't be
  confined by the structure of DA. You like messy
  solutions scribbled all over the page in every
  which direction. It's not that you want to make a
  mistake. But you really don't care that much
  about the answer. You just like the abstract
  design created by the free-wheeling solution...
  and the freedom from being confined by structure

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Dimensional Analysis - Practice

• An airplane was flown at a speed of 12,193 miles
  per hour. What was the speed of the plane in
  meters per second?

12,193 Miles 1 Hour
1 Hour 60 Minutes
1.609344 Km 1 Mile
1 Minutes 60 Seconds
X
X
X
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Dimensional Analysis - Practice

• Express the density of 5.6 g/cm3 in kg/cm3.

5.6 g 1 cm3
1 kilogram 1000 gram
X
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Dimensional Analysis - Practice

• If 20 gits equal 1 erb, and 1 futz equals 1 hews,
  and 10 erbs equal 1 futz, how many gits equal 5
  hews?