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course PHY 201
If the velocity of the object changes from 4 cm / sec to 16 cm / sec in 8 seconds, then at what average rate is the velocity changing?A ball rolling from rest down a constant incline requires 8.2 seconds to roll the 97 centimeter length of the incline.
• What is its average velocity?
An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.
• What therefore is the final velocity of this ball?
• What average rate is the velocity of the ball therefore changing?
An automobile accelerates uniformly down a constant incline, starting from rest. It requires 10 seconds to cover a distance of 132 meters. At what average rate is the velocity of the automobile therefore changing?
Average rate velocity is changing = change in velocity / change in time
Acceleration = (16 cm/sec - 4 cm/sec) / 8
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The time interval isn't 8, it's 8 seconds. So the denominator in your calculation
Acceleration = (16 cm/sec - 4 cm/sec) / 8
is not correct. The units of your answer will change when you correct the units of your denominator.
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Acceleration = 1.5 cm/sec
97 cm / 8.2 seconds = 11.8 cm/sec = average velocity
Final velocity = 2 (change in position/ change in time)
Acceleration = (final velocity - 0)/(change in clock time)
Change in average rate of velocity = ((132/10)-0)/ 10 seconds = 1.32 m/sec
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Everything is right up to here, but your calculation in the next line represents (average velocity - 0) / (10 seconds).
You haven't used units with every quantity in your calculation, so the units of your result don't follow the units of your calculation. The units of your result will not match the units of the calculation if you do include correct units throughout.
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You're on the right track, but you have to be a little more careful, especially with units.
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