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Phy 121
Your 'cq_1_08.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_08.1_labelMessages **
A ball is tossed upward with an initial velocity of 25 meters / second. Assume that the acceleration of gravity is 10 m/s^2 downward.
• What will be the velocity of the ball after one second?
answer/question/discussion: ->->->->->->->->->->->-> :
v0 = 25m/s
a = -10m/s/s
`dt = 1s
Vf = 25m/s -10m/s/s *1s
Vf= 15m/s
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• What will be its velocity at the end of two seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
v0 = 25m/s
a = -10m/s/s
`dt = 2s
Vf = 25m/s -10m/s/s *2s
Vf= 5m/s
@&
Good.
It's good to know how to use the equations, and to use the correctly, but you can also get these results from the meanings of the quantities, without using equations.
10 m/s^2 means a change of 10 m/s, every second, in the downward direction.
So starting with 25 m/s upward, after one second a change of 10 m/s downward leaves us with 15 m/s, and after another second the same change will leave us 5 m/s, still upward. After still another second the same change will bring us to 5 m/s downward, etc., etc..
*@
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• During the first two seconds, what therefore is its average velocity?
answer/question/discussion: ->->->->->->->->->->->-> :
v0 = 25m/s
vf = 5m/s
vAve= 25m/s + 5m/s / 2 = 15m/s
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• How far does it therefore rise in the first two seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
15m/s * 2s = 30m = `ds
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• What will be its velocity at the end of a additional second, and at the end of one more additional second?
answer/question/discussion: ->->->->->->->->->->->-> :
v0 = 25m/s
a = -10m/s/s
`dt = 3s
Vf = 25m/s -10m/s/s *3s
Vf= -5m/s
v0 = 25m/s
a = -10m/s/s
`dt = 4s
Vf = 25m/s -10m/s/s *4s
Vf= -15m/s
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• At what instant does the ball reach its maximum height, and how high has it risen by that instant?
The ball reaches maximum height at vf = 0 and it has risen 31m.
0m/s = 25m/s + (-10m/s^2)`dt
-25m/s = (-10m/s^2)`dt
-25m/s/(-10m/s/s) = `dt = 2.5s
`ds = 25m/s / 2 * 2.5s
`ds = 12.5m/s * 2.5s
`ds = 31m
answer/question/discussion: ->->->->->->->->->->->-> :
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• What is its average velocity for the first four seconds, and how high is it at the end of the fourth second?
Vf = -15m/s
V0 = 25m/s
vAve = (25m/s - 15m/s) /2 = 5m/s
answer/question/discussion: ->->->->->->->->->->->-> :
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• How high will it be at the end of the sixth second?
answer/question/discussion: ->->->->->->->->->->->-> :
v0 = 25m/s
a = -10m/s/s
`dt = 6s
Vf = 25m/s -10m/s/s *6s
Vf = 25m/s - 60m/s = -35m/s
`ds = (25m/s - 35m/s) / 2 * 6s
`ds = -5m/s * 6s
`ds = 30m
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** **
15 minutes
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&#Good responses. See my notes and let me know if you have questions. &#
Note that you transposed the first two numbers in your access code.
Remember my admonition to copy your access code from a reliable file rather than typing it. Though this one was fairly easy to track down, errors in codes can cause serious problems and need to be avoided.