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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.
** CQ_1_03.1_labelMessages.txt **
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: ->->->->->->->->->->->-> (start in the next line):
Average velocity for this ball is 6 cm / sec
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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: ->->->->->->->->->->->-> (start in the next line):
The final velocity would be 12 cm / sec
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By how much did its velocity therefore change?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The velocity change from 0 cm / sec (beginning) to 12 cm / sec (final velocity) so the velocity changed by 12 cm / sec
Question:
I don't know if I am understanding the question for which the velocity changes. Would it be 12 cm / sec? since the initial is 0 cm / sec and the final would be 12 cm / sec?
I looked for the idea 2.3 which says if the acceleration is uniform, v0 = 0 then vf = 2 * vAve. Since the acceleration of the ball is uniform then we could multiply 2 * 6 cm / sec which would then give us the final velocity to be 12 cm / sec
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Your reasoning is correct so far, as are your results.
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At what average rate did its velocity change with respect to clock time?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The average rate that it changed was 6 cm / sec.
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This is not correct.
You don't say how you got this.
Here's the sequence of reasoning you need to go through:
By the definition of average rate what is meant by the average rate of change of velocity with respect to clock time?
What is the change in the velocity?
What is the change in the clock time?
What therefore is the average rate of change of velocity with respect to clock time?
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What would a graph of its velocity vs. clock time look like? Give the best description you can.
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
Question:
I put down a graph that had for the x the clock time and the y value for velocity.
I started it out with 0 - 5 for clock time and velocity 0 - 12 cm.
Now the part where I am getting confused is for velocity would the line start at 0 then head to 12 cm and have the line hit it at (5 sec , 12 cm / sec - since this is the final velocity of the ball)? And that would be a straight line? And another point being at (3 sec, 6 cm / sec)?
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You would have the point (0 sec, 0 cm/sec) because the initial velocity is zero.
You also would have the point (5 sec, 12 cm/sec), as you say.
However the point (3 sec, 6 cm/sec) would not be on the line between these two points. The point (2.5 sec, 6 cm/sec) would be on the line, but you already have two points and don't really need this point.
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I don't know what the velocity would be.
I have the information that..
initial velocity = 0 cm / sec
average velocity = 6 cm / sec
final velocity = 12 cm / sec
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You also know that the change in clock time is 5 seconds.
This gives you enough information to find the average rate of change of velocity with respect to clock time.
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30 minutes
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You've got it all except for one step.
It's a very important step, so you will need to submit a revision.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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