Phy 121
Your 'cq_1_03.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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The problem:
A ball starts with velocity 0 and accelerates uniformly down a ramp of length 30 cm, covering the distance in 5 seconds.
• What is its average velocity?
answer/question/discussion: 6 cm/ sec
• If the acceleration of the ball is uniform then its average velocity is equal to the average of its initial and final velocities.
You know its average velocity, and you know the initial velocity is zero.
What therefore must be the final velocity?
answer/question/discussion: 12cm/ sec
• By how much did its velocity therefore change?
answer/question/discussion:6 cm/ sec
Your preceding questions were answered correctly, but this last question was not.
Make careful note of the following advice:
One of the most fundamental questions we can ask is the following:
What quantities are involved in this situation?
What is changing in this situation, and at what rate is it changing with respect to other quantities? (This question should be asked of all quantities)
What quantities are known in this situation?
How can the known quantities be connected to find the values of unknown quantities?
These questions will help you figure out a wide range of problems. You should make a note of these questions, and refer to whenever you are 'stuck' on a problem or unsure of your approach or you solution.
Before reading further you should answer these questions about this situation and make sure you have identified your quantities correctly, and try to use this procedure to see your error.
As soon as you know the initial and final velocities on an interval, you should automatically ask yourself the following series of questions. If you do this consistently, you will soon 'sort out' the confusions common to students when they first encounter these ideas:
What is the initial velocity on the interval?
What is the final velocity on the interval?
What therefore is the average velocity on the interval, and what is the change in velocity on the interval?
What is the definition of acceleration?
What is the definition of average velocity?
With the information given, what does knowledge of the change in velocity allow us to determine?
With the other information we know about this situation, what does knowledge of the average velocity allow us to determine?
Any time you know initial and final velocity and can't solve the problem, please feel free to submit a note to me. The note should include the information given in the problem, a copy of the above questions, and your best answer to each question (inserted in the line below the question and marked with &&&&).
• At what average rate did its velocity change with respect to clock time?
answer/question/discussion: 6 cm/ sec
In answering the questions I gave you above, you should have also addressed this question.
• What would a graph of its velocity vs. clock time look like? Give the best description you can.
answer/question/discussion: With distance down the side and clock time on the bottom the graph would be a very steep diagonal positive line going from right to left bottom to top
The velocity increases, so the v vs. t graph would slope upward.
What would be the coordinates of the initial point?
What would be the coordinates of the final point?
What would be the rise of the graph?
What would be the run of the graph?
What would be the slope of the graph corresponding to this interval?
What would be the average 'altitude' of the graph?
What would be the area beneath the graph corresponding to this interval?
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About 30 minutes
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&#Please see my notes and submit a copy of this document with revisions and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end). &#
I've just created a document which expands on the notes I've given you here. It consists of series of questions to ask yourself in various situations. I'll be adding to this document as we go through the course. I hope you find it helpful. It is posted at
http://vhcc2.vhcc.edu/dsmith/geninfo/qa_query_etc/ph1/important_advice_on_problem_solving.htm