Query_Asst_4

course Phy 201

ø‘…˜{¢]¨ü¸Šå_¡…ÒÕœÃÁÖ¦†þassignment #004

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Physics I

06-30-2006

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11:17:59

Intro Prob 6 given init vel, accel, `dt find final vel, dist

If initial velocity is v0, acceleration is a and time interval is `dt, then in symbols what are the final velocity vf and the displacement `ds?

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Given: vo, a and `dt.

since can find `dv using: `dv = a * `dt; therefore,

vf = vo + `dv

since can find vAve using: vAve = (vo +vf) / 2; therefore,

`ds = vAve * `dt

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11:19:30

**You would use accel. and `dt to find `dv:

a * `dt = `dv. Adding `dv to initial vel. vo you get final vel.

Then average initial vel. and final vel. to get ave. vel.:

(v0 + vf) / 2 = ave. vel.

You would then multiply ave. vel. and `dt together to get the distance.

For example if a = 3 m/s^2, `dt = 5 s and v0 = 3 m/s:

3 m/s^2 * 5 s = 15 m/s = `dv

15 m/s + 3 m/s = 18 m/s = fin. vel.

(18 m/s + 3 m/s) / 2 = 10.5 m/s = vAve

10.5 m/s * 5 s = 52.5 m = dist.

In more abbreviated form:

a * `dt = `dv

v0 + `dv = vf

(vf + v0) /2 = vAve

vAve * `dt = `ds so

`ds = (vf + v0) / 2 * `dt.

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11:21:16

What is the displacement `ds associated with uniform acceleration from velocity v0 to velocity vf in clock time `dt?

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`ds = [(vo + vf) / 2] * `dt

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11:21:36

** Since accel is uniform vAve = (v0 + vf) / 2.

Thus displacement is

`ds = vAve * `dt = (v0 + vf) / 2 * `dt,

which is the first equation of uniformly accelerated motion. **

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11:23:57

Describe the flow diagram we obtain for the situation in which we know v0, vf and `dt.

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Flow diagram:

given: a, `dt, vo

so from a & `dt we obtain `dv.

Then from `dv & vo we obtain vf.

Then from vf & vo we obtain vAve.

Then from 'dt & vAve we obtain `ds.

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11:24:23

** The first level in the diagram would contain `dt, v0 and vf.

Then v0 and vf would connect to `dv in the second level.

The second level would also contain vAve, connected from vf in the first level to v0 in the first level.

The third level would contain an a, connected to `dv in the second level and `dt in the first level.

The third level would also contain `ds, connected to vAve in the fourth level and `dt in the first level. **

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11:29:10

Query Add any surprises or insights you experienced as a result of this assignment.

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Another FYI: I had trouble viewing some of the videos in this assigment as well. For the Intro to Course videos on CD #2, I could not view files 3-4 at all and 2 stopped only after one minute - it stopped at the same spot each time I tried to view it and I tried many times. The rest were fine.

There is a lot of redundancy in the presentation of these ideas, since in my experience students need to see the ideas in a number of different ways before they achieve the necessary mastery. So anything you miss from a couple of videos, you will probably pick up elsewhere.

However, while students occasionally say that one video or another does not work, there has been no consistent problem with any of the videos on these CDs, and as far as I know students have always reported that when tried on a different computer, the videos work. So I think it is just a glitch with your specific computer system. A reboot might fix the problem.

On the other hand, there might be a scratch or other flaw on the CD. This is an outside chance, but if you tell me which CD and send me your address, I'll be glad to send a replacement.

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11:29:41

** Student Response: I think I really confused what information stood for what in the Force and Pendulum Experiment. However, I enjoy doing the flow diagrams. They make you think in a different way than you are used to. INSTRUCTOR NOTE: These diagrams are valuable for most people. Not all--it depends on learning style--but most. **

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Query_Asst_4

You did well on these questions. See my note related to the CD and let me know if you have questions.