Assignment 4

course PHY 231

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004. `Query 4
Physics I
07-13-2008

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01:33:53
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 -->
vf = d / t
ds = avg V * t
confidence assessment: 1

Right idea, but:

In a calculus-based course you don't want to use d for anything but differential notation (`d stands for Delta, `dt stands for Delta-t, 'dv/'dt stands for the average rate of change of velocity with respect to clock time, dv/dt is the instantaneous rate of change).

vf is not equal to d / t in any case.

t is clock time, which could be measured from any reference instant. It doesn't belong by itself in the denominator of any rate-related calculation.

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01:34:08

**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 -->

self critique assessment: 2

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01:34:40

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

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RESPONSE -->

ds = AvgV x t

Avg V = (Vo + Vf) / 2

confidence assessment: 2

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01:34:47

** 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 -->

self critique assessment: 2

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01:35:16

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

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RESPONSE -->

vO is the inital velocity, vF is the final velocity, and dt is change in time.

confidence assessment:

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01:35:39

** 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 -->

I do not understand what we are talking about when we mean levels.

self critique assessment: 2

Look at the flow diagrams for various situations as depicted in Class Notes and Introductory Problem Sets. The information generally flows downward. Given information is at the top, at the 'first level'. Quantities that follow from the given quantities are lower on the page, at 'lower levels'. The information at each level comes from the information 'above'.

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01:36:08

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

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RESPONSE -->

This assignment was strictly symbols and I did not understand what was meant by the flow level.

confidence assessment: 2

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01:36:34

** 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 -->

self critique assessment: 2

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Assignment 4

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Good responses. See my notes and let me know if you have questions. &#