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phy 121
Your 'cq_1_07.1' 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 falls freely from rest at a height of 2 meters. Observations indicate that the ball reaches the ground in .64 seconds.
Based on this information what is its acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
`ds = (vf + v0) / 2 * `dt
`ds / (vf + v0) = 2(`dt)
vf - v0 = 2(`dt)(`ds)
vf = 2(`dt) (`ds) -v0
= 2(.64s)(2m) - 0
= 2.56 m/s
The units of the preceding step are s * m, not m/s. This should have tipped you off to an error.
You didn't do the algebra correctly in solving for vf. You can't get from
`ds / (vf + v0) = 2(`dt)
to
vf - v0 = 2(`dt)(`ds).
Dividing `ds / (vf + v0) = 2(`dt) by `ds would give you
1 / (vf + v0) = 2(`dt) / `ds.
This wouldn't be particularly helpful.
To solve correctly:
Starting with
`ds = (vf + v0) / 2 * `dt
multiply both sides by 2, then divide both sides by `dt, then subtract v0 from both sides.
a = (vf - v0) / `dt
= (2.56 m/s - 0 ) / .64 s
= 4 m/s^2
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Is this consistent with an observation which concludes that a ball dropped from a height of 5 meters reaches the ground in 1.05 seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
?????I am not sure what I need to do to see if these last 2 questions are constistent.
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Are these observations consistent with the accepted value of the acceleration of gravity, which is 9.8 m / s^2?
answer/question/discussion: ->->->->->->->->->->->-> :
????
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30 min
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Do submit a revision. Good strategy but you had some errors in detail.
&#See any notes I might have inserted into your document. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#