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Phy 121
Your 'cq_1_08.2' 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 ball is tossed upward at 15 meters / second from a height of 12 meters above the ground. Assume a uniform downward
acceleration of 10 m/s^2 (an approximation within 2% of the 9.8 m/s^2 acceleration of gravity).
How high does it rise and how long does it take to get to its highest point?
answer/question/discussion: ->->->->->->->->->->->-> :
y=(v^2-vo^2)/2a=(0-15m/s)^2/2*(-10m/s^2)=11.25m the highest point
t=vo/a=(15m/s)/-10m/s^2=1.5s time to reach highest point
@& Good.*@
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How fast is it then going when it hits the ground, and how long after the initial toss does it first strike the ground?
answer/question/discussion: ->->->->->->->->->->->-> :
I understand the velocity when the ball returns to original place, the velocity is the same as the initial velocity, which
would be 15m/s. Is that true in this case?
@& That is the case, but the question asks about the time at which the ball reaches the ground, which is not at the same vertical position from which it was tossed.*@
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At what clock time(s) will the speed of the ball be 5 meters / second?
answer/question/discussion: ->->->->->->->->->->->-> :
@& The downward acceleration 10 m/s^2 indicates that the ball's velocity decreases by 10 m/s every second.
What then will be its velocities at, say, the ends of each of the next 4 seconds? What therefore will be the speeds at these times?
It doesn't require equations to answer this question. It would be possible to answer using equations, but in this case it's better not to resort to equations.
*@
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At what clock time(s) will the ball be 20 meters above the ground?
@& This one would require the use of equations.
Consider the interval from release until reaching the 20 meter position.
You know the acceleration and the initial velocity. Among the other variables `dt, vf and `ds, which do you know?
Knowing these three quantities, which equation or equations would allow you to find a fourth?
Having found a fourth, it would then be possible to directly reason out the fifth.*@
How high will it be at the end of the sixth second?
answer/question/discussion: ->->->->->->->->->->->-> :
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2 hours
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I have attempted one question which I don't think is correct. The other questions I understand but have no idea how to solve.
@& Don't get bogged down on this, but spend up to 20 minues giving the best answers you can to my questions. You might well get everything within that time frame, but if not submit what you can and we'll go from there.
I don't think it will be difficult for you to clear this up.
&#Please see my notes and, unless my notes indicate that revision is optional, 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.
If my notes indicate that revision is optional, use your own judgement as to whether a revision will benefit you. &#