practice work

course PHY 121

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Physics I Class Notes

12-08-2007

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18:09:58

Given the initial velocity, final velocity and time duration of a uniformly accelerating object, how do we reason out the corresponding acceleration and change in the position of an object?

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RESPONSE -->

duration is related to the velocity at which an object is moving with respect to gravity and initial velocity

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18:12:20

12-08-2007 18:12:20

** COMMON ERRONEOUS STUDENT RESPONSE: To find the average acceleration, we divide the change in veolocity by the time interval. To find the change in position or displacement of the object over any time interval multiply the average velocity over that interval by the duration of the interval.

You are not given the average velocity or the change in velocity. You have to first determine the average velocity; then your strategy will work.

Since acceleration is constant you can say that average velocity is the average of initial and final velocities: vAve = (v0 + vf) / 2.

Change in velocity is `dv = vf - v0.

Now we can do as you say:

To find the change in position or displacement of the object over any time interval multiply the average velocity over that interval by the duration of the interval. **

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NOTES -------> change in velocity is final velocity minus the initial velocity, but if we want to find the change in position of an object then we use the average velocity and multipy it by the time interval to find the displacement

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18:15:59

In terms of the meanings of altitudes, area, slope and width, how does a velocity vs. clock time trapezoid represent change in position and acceleration?

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RESPONSE -->

the different angles within the trapezoid can be manipulated so that an object within the area, slope, or whatever will change with that angle

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18:16:27

12-08-2007 18:16:27

** If you multiply the average altitude by the width (finding the area) of the trapezoid you are multiplying the average velocity by the time interval. This gives you the displacement during the time interval.

The rise of the triangle represents the change in velocity and the run represents the time interval, so slope = rise / run represents change in velocity / time interval = acceleration. **

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NOTES -------> ok

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You've saved the given solutions to notes, but haven't self-critiqued your work. You should do both.

Let me know if you have questions on any of these ideas.