phy 201
Your 'cq_1_8.2' 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?
V0 = 15m/s ds = 12m, a = 10m/s/s
The ball isn't traveling to the ground; it is going upward from the initial point.
Vf = v0 + at
T = vf-v0 /a
T = 15/10m/s/s
T = 1.5s
Y = vf^2 - v0^2 + 2ay
Y = 0 - 15m/s^2 / 2 ( 10m/s/s)
Y = 11.25m
So far everything is good; you haven't yet used the (incorrect) `ds = 12 m.
How fast is it then going when it hits the ground, and how long after the initial toss does it first strike the ground? It will hit at gravity accel which is 9.8 m/s/s and will take 3sec. To complete its cycle Y = y0+ v0t + .5at^2
15m = 0 + 15t +.5(10m/s/s)t
T = 15 m/s +- sort (15^2 - 4* 5m/s/s * 12m / 2 (5m/s/s)
The 12 m doesn't appear in your first equation; it has just appeared in your solution.
You've included the units on most, but not all of your quantities. However the units are not included in the lines below.
T = 15 +- (-15) /10
T = 30/10 = 3
T = 0/10 = 0
At what clock time(s) will the speed of the ball be 5 meters / second?
Vave = v0 + vf /2
Vave = 0 + 15/2 = 7.5
T = change in position /vAve
T = 12/7.5 = 1.6
Good reasoning, but the 7.5 m/s average velocity doesn't apply to a 12 m displacement.
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:
T = a2 + b + c
T = 15+- sort ( 15m/s^2 - 4 (5) * 20m / 2*5
T = 15+- sort 175 / 2 * 5
T = 15 + 13 /10
T = 2.8
It will be back in his hands at the sixth second
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20min
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Your reasoning is good throughout; as on the preceding problem there are some details that need to be corrected, but you're in very good shape to understand the details in the link below. You are doing quite well with this.
&#At least part of your solution does not agree with the solution and comments given at the link below. You should view the solution at that link and self-critique as indicated there.
Solution
This link also expands on these topics and alerts you to many of the common errors made by students in the first part of this course. &#