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course Phy 121

9/9 3:20

The problem:A ball starts with velocity 4 cm/sec and ends with a velocity of 10 cm/sec.

What is your best guess about the ball's average velocity?

answer/question/discussion (start in the next line):

10 cm/s + 4 cm/s = 14 cm/s / 2 = 7 cm/s

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Without further information, why is this just a guess?

answer/question/discussion (start in the next line):

because we are not given a time interval or the length it travels.

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If it takes 3 seconds to get from the first velocity to the second, then what is your best guess about how far it traveled during that time?

answer/question/discussion (start in the next line):

#####ave vel = (change in position) / (change in clock time)

change in position = ave vel * change in clock time

change in position = 7 cm/s * 3 s = 21 (cm/s) (s) = 21 cm

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At what average rate did its velocity change with respect to clock time during this interval?

answer/question/discussion (start in the next line):

ave rate = (change in velocity) / (change in clock time)

change in velocity = 10 cm/s - 4 cm/s = 6 cm/s

average rate of change of velocity with respect to clock time = (change in velocity) / (change in clock time)

average rate = 6 cm/s / (2 s) = 3 cm/s^2

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