phy201
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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: ->->->->->->->->->->->-> :
vf= 25m/s+ 10 m/s^2(1s)= 35m/s
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• What will be its velocity at the end of two seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
vf= 25m/s+ 10 m/s^2(2s)= 45m/s
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• During the first two seconds, what therefore is its average velocity?
answer/question/discussion: ->->->->->->->->->->->-> :
vAve= ( 25m/s +45m/s)/2= 35m/s
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• How far does it therefore rise in the first two seconds?
answer/question/discussion: ->->->->->->->->->->->-> :
`ds= vAve*`dt so `ds= 35m/s * 2s= 70m
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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: ->->->->->->->->->->->-> :
vf@3s= 25m/s+ 10 m/s^2(3s)= 55m/s
vf@4s= 25m/s+ 10 m/s^2(4s)= 65m/s
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• At what instant does the ball reach its maximum height, and how high has it risen by that instant?
answer/question/discussion: ->->->->->->->->->->->-> :
'ds= (vf^2-v0^2)/2a so `ds= ((0m/s)^2- (25m/s) ^2)/2 (-10m/s^2)= -625/ -20= 31.25 m
vf= v0+at so 0= 25m/s+-10m/s^2 (t) = -25m/s=-10m/s^2= 2.5s
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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?
answer/question/discussion: ->->->->->->->->->->->-> :
vAve= (65m/s + 25m/s)/2= 45m/s
`ds= 45m/s* 6s= 180m
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• How high will it be at the end of the sixth second?
answer/question/discussion: ->->->->->->->->->->->-> :
vf@6s= 25m/s+ 10 m/s^2(6s)= 85m/s
vAve= (85m/s +25m/s)/2= 55m/s
55m/s * 6s= 330m
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1hour
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I don't know if I calculated a lot for this wrong but my answers do not seem to make sense logically. If the max height occurs 2.5s and is 31.25m then why are the other answers not consistent with that? I got that the height at 2s was 70 m and that can't be correct but I don't know what I did wrong. It seems to me that after 2.5 s the ball would start traveling back toward the ground so should my heights have been negative numbers? I don't even know if that would make since the height i got at 6 seconds far surpasses the distance it would take to travel the max height and hit the ground again. Can you explain it to me please?
Your calculations are all good, except that gravity accelerates the ball downward. Whatever sign you choose to use for your initial velocity, the gravitational acceleration must be of opposite sign.
This should be easy to correct, but if not be sure to ask questions.
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