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Phy 121
Your 'cq_1_22.2' 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 70 gram ball rolls off the edge of a table and falls freely to the floor 122 cm below. While in free fall it moves 40 cm in the horizontal direction. At the instant it leaves the edge it is moving only in the horizontal direction. In the vertical direction, at this instant it is moving neither up nor down so its vertical velocity is zero. For the interval of free fall:
What are its final velocity in the vertical direction and its average velocity in the horizontal direction?
answer/question/discussion: ->->->->->->->->->->->-> :
First found vfVert: vfVert = sqrt(0 m/s + 2 * 9.8 * .122 m/s) = 1.54 m/s = 1540 cm/s.
.122 m/s is not a displacement. The displacement is 1.22 m.
Second found 'dt: vAveVert = vf+v0 / 2 = 'ds/'dt, so, 1.54m/s / 2 = .122 m / 'dt. 'dt = .158 seconds.
Third find vAveHorz: 0.04 m / .158 s = .253 m/s = 253 cm/s
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Assuming zero acceleration in the horizontal direction, what are the vertical and horizontal components of its velocity the instant before striking the floor?
answer/question/discussion: ->->->->->->->->->->->-> :
If there is no acceleration then the initial velocity = final velocity = average velocity. So the velocity vectors are: vx = .253m/s vy = 1.54 m/s
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What are its speed and direction of motion at this instant?
answer/question/discussion: ->->->->->->->->->->->-> :
Speed = sqrt(.253^2 m/s + 1.54^2 m/s) = 1.56 m/s
arctan(.253m/s / 1.54m/s) = 9.3 degrees
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What is its kinetic energy at this instant?
answer/question/discussion: ->->->->->->->->->->->-> :
KE = 1/2 * .007 kg * 1.56 m/s = 0.00546 J
This seems low, but if my numbers are right then this has to be right.
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What was its kinetic energy as it left the tabletop?
answer/question/discussion: ->->->->->->->->->->->-> :
The only velocity at the time was in the horizontal direction so the KE = 1/2 * .007 kg * .253 m/s = 8.8 * 10^-4
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What is the change in its gravitational potential energy from the tabletop to the floor?
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How are the the initial KE, the final KE and the change in PE related?
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How much of the final KE is in the horizontal direction and how much in the vertical?
answer/question/discussion: ->->->->->->->->->->->-> :
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I started to get a little lost after my KE and PE numbers did not add up or seem to make since. I will have to look at the solutions to critique myself.
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122 cm is 1.22 m, not .122 m. This threw you off. There were a couple of other things too. Do submit a revision on this one, just to be sure you've got it.
&#See any notes I might have inserted into your document, and before looking at the link below see if you can modify your solutions. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your old and new 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. &#