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phy 201
Your 'cq_1_08.1' 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_08.1_labelMessages **
A ball is tossed upward with an initial velocity of 25 meters / second. Assume that the acceleration of gravity is 10 m/s^2 downward.
• What will be the velocity of the ball after one second?
answer/question/discussion: ->->->->->->->->->->->-> :
a = 25m/s / 1s = 25m/s^2 - 10m/s^2 = 12 m/s^2
12m/s
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If the velocity of an object changed by 25 m/s in 1 s then the acceleration would be 25 m/s^2.
So the statement
a = 25m/s / 1s = 25m/s^2
would be correct.
However it would not apply to this situation because nothing is changing velocity by 25 m/s in a 1 second interval.
Note also that your statement
a = 25m/s / 1s = 25m/s^2 - 10 m/s^2
is not in any case correct. 25 m/s / (1 s) = 25 m/s^2, not 25 m/s^2 - 10 m/s^2.
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What you know is that the acceleration is 10 m/s^2 downward, and you know that the object's initial velocity is 25 m/s upward.
What can you conclude about what happens (e.g., what changes, and by how much) during the next second?• What will be its velocity at the end of two seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
25m/s 2s = 12.5m/s^2 -10m/s^2 = 2.5m/s^2
2.5m/s^2 * 2sec = 5m/s
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Nothing in this situation changes velocity by 25 m/s in 2 s.
See also my note on the preceding.
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• During the first two seconds, what therefore is its average velocity?
answer/question/discussion: ->->->->->->->->->->->-> :
Vave = (5m/s + 25m/s) / 2
=15m/s
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This turns out to be correct. However the reasoning you used to get 5 m/s is not correct, and in another situation would not lead to a correct conclusion.
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• How far does it therefore rise in the first two seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
15m/s = `ds/2s
30meters
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The 15 m/s average velocity is correct, though you didn't find it by a correct ling of reasoning.
This result does follow correctly from the 15 m/s average velocity; your reasoning on this step was fine.
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• What will be its velocity at the end of a additional second, and at the end of one more additional second?
answer/question/discussion: ->->->->->->->->->->->-> :
25m/s/3sec = 8.3m/s^2
8.3 - 10 = -1.6
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This result is not correct. See my earlier notes.
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• At what instant does the ball reach its maximum height, and how high has it risen by that instant?
answer/question/discussion: ->->->->->->->->->->->-> :
after two seconds and before three
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• What is its average velocity for the first four seconds, and how high is it at the end of the fourth second?
answer/question/discussion: ->->->->->->->->->->->-> :
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• How high will it be at the end of the sixth second?
answer/question/discussion: ->->->->->->->->->->->-> :
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** **
30min
** **
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You used some incorrect reasoning on this problem.
&#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).
Be sure to include the entire document, including my notes. &#
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