Query 4

course Phy 201

qwqÐԼ알zŅ}ڝassignment #004

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004. `Query 4

Physics I

05-27-2007

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23:14:01

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 -->

Since we know a, 'dt, and vo, we can use these to find vf.

A=vf-vo/'dt

A*'dt=vf-vo

A*dt+vo=vf

Vf+vo/2=vAve

vAve='ds/'dt

vAve*'dt='ds

confidence assessment: 1

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23:14:51

**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 -->

Yay. I had no confidence in this, but I got it right. Instead of combining vo and vf as 'dv, I used them separately.

self critique assessment: 3

Excellent reasoning. But watch your grouping and order of operations:

a=(vf-vo)/'dt

(Vf+vo)/2=vAve

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23:16:38

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

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RESPONSE -->

aAve=vf-vo/'dt

vf-vo/2=vAve

vAve='ds/'dt

vAve'dt='ds

I hope this is what the question was asking. I am a little bit unsure what I am ""solving for.""

confidence assessment: 1

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23:17:28

** 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 -->

Okay, I understand.

self critique assessment: 3

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23:19:41

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

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RESPONSE -->

Well, vo and vf can be used to find, in conjunction with 'dt, either aAve or vAve.

To find aAve, one must find 'dv and divide it by 'dt.

To find vAve, one must add vo and f and divide by two. The, one must use the formula vAve='ds/'dt

vAve*'dt='ds to complete this formula.

confidence assessment: 3

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23:20:09

** 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 -->

Okay, guess I don't know what a flow chart is! I understand the concepts behind the material, though.

self critique assessment: 2

You explained it correctly. But be sure to see the Introductory Problem Sets for the flow diagram idea. It can be very helpful in picturing the relationships among the variables. Also you're expected to know it on the first test/major quiz.

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23:21:03

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

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RESPONSE -->

This helped me a LOT to be able to utilize small portions of information to make larger connections. I worried that I was not able to actually do it myself, but this assignment has given me some confidence.

confidence assessment: 3

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23:21:27

** 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 -->

Flow charts definately are not ""it"" for me, but I will try to use them to help me... I might be surprised!

self critique assessment: 2

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Good work. See my notes and let me know if you have questions.