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: ->->->->->->->->->->->-> :
I used the equation y = v2-V0^2/2a
I put in the following y= (0-15m/s)^2/2(-10m/s^2)
I came up with -225m^2/s^2/-20m/s^2
Very good application of the equation.
The object rises 11.25m.
Would this number need to be added to 12 m since this is the height the object was when it was thrown upwards??? If so then the maximum height would have been 23.25m.
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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 assumed that if we were trying to find out how fast the ball was going when it hit the ground that we would need the distance from its highest point to the ground. This would have a value of zero. So our total change in velocity would be 23.25m/s. We now need to divide this by 10m/s^2. It gives us an answer of 2.325m/s.
23.25 m/s / (10 m/s^2) = 2.325 seconds, not 2.325 m/s.
`dv / a gives you `dt, not a velocity.
The time would be 15m/s/.5m/s^2 = 3s.
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• At what clock time(s) will the speed of the ball be 5 meters / second?
answer/question/discussion: ->->->->->->->->->->->-> :
I used 5m/s/10m/s^2 and came up with .05 seconds.
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• 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 used the quadratic formula on this and got +-1s or +-2seconds.
At the end of the 6th second it would be 80 meters above the ground.
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2 h+
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I found this work particularly tricky and reworked it several times. I am still not confident in my given answers.
Very good attempts, with some nice successes. You also had some errors, but I believe you're on the verge of getting everything sorted out.
&#Please compare your solutions with the expanded discussion at the link
Solution
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