cq_1_082

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Phy 231

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: ->->->->->->->->->->->-> :

vf = v0 + a * t

0 = 15 -10 * t

t = 1.5 s

y-y0 = v0 * t + 0.5 * a * t^2

y-12 = 15 * 1.5 + 0.5 * -10 * 1.5^2

y = 15 * 1.5 + (0.5 * -10 * 1.5^2) + 12

y = 23.25 m

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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: ->->->->->->->->->->->-> :

x-x0 = v0 * t + 0.5 * a * t^2

-23.25 = 15 * t + 0.5 * -10 * t^2

t = 4.13 s

vf = v0 + a * t

vf = 15 - 10 * 4.13

vf = 26.3 m/s downward

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At what clock time(s) will the speed of the ball be 5 meters /

second?

answer/question/discussion: ->->->->->->->->->->->-> :

v = v0 + a * t

5 = 15 + -10 * t

t = 1.0 sec

@& Speed is 5 m/s if the velocity is 5 m/s or -5 m/s. You didn't consider the latter. Easily done, of course, but not as easy to remember to consider it.*@

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&#Good responses. See my notes and let me know if you have questions. &#