course Phy121
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If the velocity of the object changes from 3 cm / sec to 13 cm / sec in 7 seconds, then at what average rate is the velocity changing?
vAve = `ds/`dt for this problem, 10cm (`ds)/7 s(`dt) = 1.4 cm/s
You aren't given `ds. You are given two values of the velocity v.
Also, the question doesn't ask for vAve, it asks for the average rate of change of velocity (implicitly the average rate of change of velocity with respect to clock time).
This rate is change in vel / change in clock time, i.e., `dv / `dt. Note also that `dv does not have units of cm.
Can you send me a correction?
Be very careful of your units for the ave rate.
A ball rolling from rest down a constant incline requires 9.6 seconds to roll the 99 centimeter length of the incline.
* What is its average velocity?
As above, 99cm/9.6s = 10.3 cm/s for vAve
Good, but this is different from the above. Here you are given `ds.
Note: best to separate your answer from the question by a couple of spaces; much easier for the reader to make out where the question ends and where the answer begins
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? vF=10.3cm/s*2 = 20.6 cm/s
* What average rate is the velocity of the ball therefore changing? Acceleration is `dv/`dt, or 20.6 cm/s/9.6s = 2.14 cm/s^2
Good.
An automobile accelerates uniformly down a constant incline, starting from rest. It requires 16 seconds to cover a distance of 120 meters. At what average rate is the velocity of the automobile therefore changing?
vAve = 120m/16s = 7.5 m/s
This is the average velocity, not the average rate of change of velocity.
Good work on the 'middle' series of questions, but you misinterpreted the first and last questions. Please send me a revised solution of each of those two (and/or questions, if you have them).