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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A ball starts with velocity 0 and accelerates down a ramp of length 30 cm, covering the distance in 5 seconds.
• What is its average velocity?
o vAve=`ds/`dt
o vAve=30 cm/5seconds
o vAve = 6 cm/sec
Answer/question/discussion:
• If the acceleration of the ball is uniform then its average velocity is equal to the average of its initial and final velocities.
o Yes, I understand that uniform refers to the fact that the velocity is the same throughout the run.
Answer/question/discussion:
• You know its average velocity, and you know the initial velocity is zero. What therefore must be the final velocity?
o 12 cm/sec
Answer/question/discussion:
• By how much did its velocity therefore change?
o It increased steadily throughout the experiment, in a uniform fashion. It must have been 12 cm/sec at the end because then the average would turn out to be 6 cm/sec.
You have the correct average velocity, but haven't answered the question posed here.
The question asked by how much the velocity changed.
What was the velocity at the beginning of the interval?
What was the velocity at the end of the interval?
What therefore was the change in velocity?
Answer/question/discussion:
• At what average rate did its velocity change with respect to clock time?
o Although I am unsure of how to answer this, I will make my best guess.
o vAve * `ds = `dt
vAve = `ds / `dt; solving for `dt you would get `dt = `ds / vAve.
However this doesn't answer the question. See my next note.
Also note that 6 cm/s * 30 cm would be 180 cm^2 / s, not 180 cm/s^2.
o 6cm/sec * 30 cm = dt
o 180 cm/sec^2 = dt ( I am not sure how to solve this!)
You need to apply the definition of the average rate of change of velocity with respect to clock time.
What is this definition?
What is the change in velocity?
What is the change in clock time?
What is the average rate of change of velocity with respect to clock time?
Answer/question/discussion:
• What would a graph of its velocity vs. clock time look like? Give the best description you can.
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25 minutes
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I am still having trouble with the average rate and how velocity changes with respect to the clock time.
On every problem you should start by writing down the definition of average velocity and the definition of average acceleration. You should also include a short note that if acceleration is uniform, then average velocity is the average of the initial and final velocities. Any uniformly accelerated motion problem can be reasoned out from these three things.
Under Assignment 5 there is a link entitled 'synopsis of principles and common errors in analysis of motion'. You're far enough along to take a look at that document now. If you find it useful you might want to look at it every once in awhile.
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