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course Phy 241
7/4/2013 1:50 pm
If the velocity of the object changes from 3 cm / sec to 11 cm / sec in 9 seconds, then at what average rate is the velocity changing?A ball rolling from rest down a constant incline requires 8.6 seconds to roll the 68 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 15 seconds to cover a distance of 172 meters. At what average rate is the velocity of the automobile therefore changing?
The average rate at which the velocity is changing is found by (11cm/s-3cm/s)/9s = 8cm/s/9s ≈ 0.889 cm/s
The average velocity of a ball rolling from rest down a constant incline that requires 8.6s to roll 68cm is 68cm/8.6s ≈ 7.91cm/s
The final velocity would be ≈ 15.81cm/s
The velocity of the ball is changing at an average rate of 15.81cm/s/8.6s ≈ 1.84cm/s
The average rate at which the velocity of the automobile is changing is found by:
172m/15s ≈ 11.467m/s
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This is the average rate at which position is changing.
You do need this, but the problem asks for the average rate at which the velocity changes.
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