#$&*
PHY 121
Your 'cq_1_08.2' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_08.2_labelMessages **
A ball is tossed upward at 15 meters / second from a height of 12 meters above the
ground. Assume a uniform downward acceleration of 10 m/s^2 (an approximation within 2%
of the 9.8 m/s^2 acceleration of gravity).
How high does it rise and how long does it take to get to its highest point?
answer/question/discussion: ->->->->->->->->->->->-> :
I believe that it will go 24.5 m. This is because during the first second, the initial
velocity is 15 m/s and it loses 10 m/s due to gravity. This makes the final velocity of
this segment 5 m/s. This averages to 10 m/s, so it is up 12 + 10 = 22. Then it starts
this part at 5 m/s, but the gravity pulls at 10 m/s, so it will only go up half-way.
But the average velocity for this segment is 5/2, or 2.5. That makes the total 24.5 m.
#$&*
@&
Very good thinking, but there is an error. From +5 m/s to -5 m/s the average velocity is 0 (as it must be since the ball is at the same height at both times).
The ball reaches its max height at the instant it comes to rest. Thus:
It takes 1.5 sec for the velocity to reach zero, during which ave velocity is (15 m/s + 0 m/s) / 2 = 7.5 m/s.
7.5 m/s * 1.5 s = 12.25 meters.
*@
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: ->->->->->->->->->->->-> :
It's going 25 m/s and it is 4 seconds after the original toss. All this is from my
picture, not math.
#$&*
At what clock time(s) will the speed of the ball be 5 meters / second?
answer/question/discussion: ->->->->->->->->->->->-> :
It will be at 5 m/s at 1 second in and at 2 seconds in.
#$&*
At what clock time(s) will the ball be 20 meters above the ground?
How high will it be at the end of the sixth second?
answer/question/discussion: ->->->->->->->->->->->-> :
I guess I am hopelessly lost at this point. Now I'm trying math, but it's letting me
down. I know that I'm missing something that probably simple. But I can't seem to find
it. I don't usually give up, but I'm flummoxed!
#$&*
*#&!*#&!
&#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. &#