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course Phy 231

HzЀpҾvѮassignment #001

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Liberal Arts Mathematics I

09-24-2008

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assignment #004

004. `Query 4

Physics I

09-24-2008

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22:26:53

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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RESPONSE -->

ds=a*dt, vf=v0+adt

confidence assessment: 2

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22:28:38

**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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RESPONSE -->

You could get final velocity by taking the inital velocity and adding the the change in velocity dv.

self critique assessment: 2

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22:31:30

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

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RESPONSE -->

(vf + v0)/2 = average velocity, average velocity * dt = ds.

confidence assessment: 3

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22:31:48

** 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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RESPONSE -->

OK

self critique assessment: 3

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22:34:46

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

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RESPONSE -->

We have v0 vf and dt in different boxes. We then have a line from both v0 and vf connecting to vAve. We then have a line coming from vAve and a line from dt going into ds.

confidence assessment: 2

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22:35:42

** 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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RESPONSE -->

My flow diagram was eally for the previous problem but I have the same idea.

self critique assessment: 2

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22:38:13

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

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RESPONSE -->

I thought the lab experiment with the one skinny rubber band and one fat rubber band was pretty cool. The smaller rubber band had a large change in length at first and it's rate of change of length got smaller and smaller as I stretched it further. The ruler lab was a pain. I saw the point of it but it was very long.

confidence assessment: 3

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22:38:27

** 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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RESPONSE -->

OK

self critique assessment: 3

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Good work.

Thanks for the comments on the labs. What a rubber band approaches its elastic limit, it takes a lot more force to add a little bit of stretch, which is consistent with your observation.

I'd like to further shorten the ruler lab, especially for students who know what they're doing. Most students need the experience of making these measurements, because most have never been challenged to make precise measurements, but for those who have I certainly agree that a shorter lab would be more appropriate.