1. Created for CVCA Physics by Dick Heckathorn 24 March 2K + 5
Problem Solving
Created for CVCA Physics by
Dick Heckathorn
24 March 2K + 5

2. Objectives We will learn how to:
use the GUESS method to solve problems.
use units when solving problems.
convert from one unit to another.

3. Step One Read the Problem
This means reading the problem for understanding, not just looking at words.
In reading one may wish to draw a diagram to help develop a visual picture of what is going on.

4. Step Two Understand The Words
Make sure that you know the meaning of all words used in the problem.
Pay particular attention to words that have unique meaning(s).

5. The Problem to be Solved
This morning your instructor traveled 26.4 miles from his home to CVCA in 0.6 hours.
Find his average speed in miles per hour.
Do you have a good idea of what is going on?

6. You will now be introduced to a method of solving this problem using the
G U E S S
method.

7. The Letters Stand For: G - Given U - Unknown E - Equation
S - Substitute
S - Solve

8. As you proceed through this five step process, you will need to write all the necessary information on a piece of paper as you complete each step.

9. When the last step is completed, you will have the solution along with your work showing how you arrived at the answer.

10. Remember, your instructor feels that the steps you use to solve the problem are more important than the answer.
Therefore he insists that you show each step!!!

11. Sounds easy so let’s begin.

12. The Problem Stated Again
This morning your instructor traveled 26.4 miles from his home to CVCA in 0.6 hours.
Find his average speed in miles per hour.

13. Your First Step
Find a given quantity?

14. Identifying a Given Quantity
One Given quantity is 26.4 miles which represents a distance.
One always represents distance with a 'd’.
Note… this is a small 'd ’.

15. Properly Writing a Given Quantity
d = 26.4 miles
Note… the unit ‘miles’ must be included.

16. The Problem Stated Again
This morning your instructor traveled 26.4 miles from his home to CVCA in 0.6 hours.
Find his average speed in miles per hour.

17. Are there other Given quantities?
The answer is yes so:

18. Identifying a second Given (G)
A second Given quantity is 0.6 hours which represents a quantity of time.
One always uses 't' for time.
Note that this is a small 't’.

19. Adding a Second Variable
Thus one adds to:
d = 26.4 miles
t = 0.6 hours
a second variable

20. Are there any other Given quantities?

21. The Problem Stated Again
This morning your instructor traveled 26.4 miles from his home to CVCA in 0.6 hours.
Find his average speed in miles per hour.

22. The answer is no.
So on to the next step.

23. Identifying the Unknown (U)
The unknown is ‘speed’ which is represented by the letter ‘v’.
Note… this is a small ‘v’.

24. Adding the Unknown Variable
d = 26.4 miles
t = 0.6 hour
v = ______

25. A Problems That Must Be Addressed
Note…Many if not all of you will think the word ‘rate’ represents how fast something is moving. While this is the word used in math classes for this purpose, it is not used for this purpose in physics.

26. A Challenge
Your instructor will expect you to work hard to omit the word ‘rate’ when describing how fast something is moving and instead, use the word ‘speed’.

27. Speed vs Velocity
There is another word, ‘velocity’, which also describes how fast something is moving.
It’s definition differs from ‘speed’.
Stay tuned for the definition of ‘velocity’.

28. Identifying the Equation (E)
The 3rd step in solving a problem is to identify the Equation that relates the
Given quantities (d) and (t) to the
Unknown quantity (v).

29. One might have learned that:
and in symbol form:

30. Adding the (E)quation
d = 26.4 miles
t = 0.6 hours
v = ______

31. Substituting (S) variables into the Equation
The 4th step is to substitute the variables (d) and (t) into the equation:

32. Your Work so Far
d = 26.4 miles
t = 0.6 hours
v = ______

33. Solving (S) to find the answer.
The 5th step is to Solve the problem.
To do this one performs the necessary calculation usually using a calculator.

34. Your Work for this Problem
d = 26.4 miles
t = 0.6 hours
v = ______

35. Note that the units are written in fraction form with a distinct numerator and denominator. There are never to be written as:

36. Your Final Written Product
d = 26.4 miles
t = 0.6 hours G
v = ______ U E S S

37. A Question
“Does the answer seem reasonable?”

38. Another Question
Do the units of the answer appear to be correct based on the information given?

39. Remember that the units talk.
But they can ‘talk’ only if you faithfully keep track of them.
Failure to do so will cause your instructor extreme disappointment.
In fact it will cause point loss beginning with the first step omitted.

40. In solving this problem, the units help to tell us if we are correct or not.
Since the units are identical to that which were identified in the unknown statement, one can safely conclude that the problem was set up and solved correctly.

41. There is a possibility that one made a careless mistake, but this is generally not the case.
Your instructor will remind you and remind you and remind you…
“Let the Units Do the Talking.”

42. Units Are Important!!!
Since they talk, be sure to listen for they say much.
But remember, they will not talk unless they are available. So faithfully keep track of them.

43. The Problem Changed Slightly
This morning your instructor traveled 26.4 miles from his home to CVCA in 36 minutes.
Find his average speed in miles per hour.

44. Will expressing the time in minutes change how one does the problem?
The answer is yes, so lets see the difference.

45. The variable ‘d’ -> 26.4 miles is the same.

46. Your Work so Far
d = 26.4 miles

47. The known variable ‘t’ is expressed as 36 minutes.

48. Your Work so Far
d = 26.4 miles
t = 36 min

49. Identifying the Unknown (U)
The unknown is ‘speed’ which is represented by the letter ‘v’.

50. Your Work so Far
d = 26.4 miles
t = 36 min
v = ______

51. Using the same (E)quation
d = 26.4 miles
t = 36 min
v = ______

52. Substituting Variables into the Equation
One still substitutes the variable for time into the equation using the unit given.

53. Your Work so Far
d = 26.4 miles
t = 36 min
v = ______

54. Since the units are not the units desired, one must change minutes into hours.
To be able to do this one needs to know an identity that relates minutes to hours.

55. I think all of us know that:
60 minutes = 1 hour
At this point we need to make the identity into a fraction.
To do so, one gets either or

56. What is the value of either fraction? Stop and think before going on!
If you said one, then you are correct for the value of the item in the numerator equals the value of the item in the denominator.

57. Which fraction you will multiple the variables in the equation by for correct unit analysis?

58. You should choose:
Doing so will give:

59. Performing the calculations gives the answer:
One will next cancel out the ‘min’ in the numerator and the ‘min’ in the denominator.
Performing the calculations gives the answer:

60. It is not uncommon for most students to convert the 36 minutes to 0
It is not uncommon for most students to convert the 36 minutes to 0.6 hours when they identify it as a given.
Your instructor wishes that you get in the habit of NOT converting until the need arises.

61. And there you have it. You have learned how to:
use the GUESS method to solve problems.
use units when solving problems.
convert from one unit to another.

62. Then ask your instructor for assistance. Thank you and happy learning.
As you go through this tutorial, please make note of anything that is not clear.
Then ask your instructor for assistance.
Thank you and happy learning.