PH1 Query 7

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course PHY 201

10/01/2011 12:26 PM

007. `query 7

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Question: `qDescribe the flow diagram you would use for the

uniform acceleration situation in which you are given v0, vf, and

`dt.

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Your solution:

From v0 and vf we can find vAve and 'dv, now knowing vAve and 'dt

we can find 'ds, also knowing 'dv and 'dt we can find a.

confidence rating #$&*: 3

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Given Solution:

We start with v0, vf and `dt on the first line of the diagram.

We use v0 and vf to find Vave, indicated by lines from v0 and vf

to vAve.

Use Vave and 'dt to find 'ds, indicated by lines from vAve and

`dt to `ds.

Then use `dv and 'dt to find acceleration, indicated by lines

from vAve and `dt to a. **

STUDENT COMMENT i dont understand how you answer matches up with

the question

INSTRUCTOR RESPONSE All quantities are found from basic

definitions where possible; where this is possible each new

quantity will be the result of two other quantities whose value

was either given or has already been determined.

Using 'dt and a, find 'dv (since a = `dv / `dt, we have `dv = a

`dt).

Using 'dv and v0, find vf, indicated by lines from `dv and v0 to

vf (vf = v0 + `dv).

Using vf and v0, find vAve, indicated by lines from vf and v0 to

vAve ( (vf + v0) / 2 = vAve, for uniform acceleration).

Using 'dt and vAve, find 'ds, indicated by lines from `dt and

vAve to `ds (vAve = `ds / `dt so `ds = vAve * `dt).

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Self-critique (if necessary):

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Self-critique Rating:OK

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Question: Describe the flow diagram you would use for the

uniform acceleration situation in which you are given `dt, a, v0

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Your solution:

Using a, 'dt, and v0 we can find vf, knowing vf and v0 we can

find 'dv and vAve, knowing vAve and 'dt we can find 'ds.

confidence rating #$&*: 3

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Given Solution:

Student Solution: Using 'dt and a, find 'dv.

Using 'dv and v0, find vf, indicated by lines from `dv and v0 to

vf.

Using vf and v0, find vAve, indicated by lines from vf and v0 to

vAve

Using 'dt and vAve, find 'ds, indicated by lines from `dt and

vAve to `ds.

STUDENT QUESTION

Can you only have two lines that connect to one variable because

i utilized the formula vf=v0 +a `dt and connected all three

to find vf? I do see how it could be done using two in the above

solution.

INSTRUCTOR RESPONSE

The idea is to use the definitions of velocity and acceleration

whenever possible. This is possible in this case:

If you know `dt and a you can use the definition of acceleration

to find `dv (which is equal to a `dt).

Then you can use v0 and `dv to get vf (which is equal to v0 +

`dv; from this you could conclude that vf = v0 + a `dv).

You end up with the same result you would have gotten from the

formula, but you are using insight into the nature of velocity

and acceleration by using the definitions, as opposed to a

memorized formula that can be applied whether or not you

understand its meaning.

The only exceptional cases are when you know v0 or vf (but not

both), acceleration a and displacement `ds. In that case you

need to start with the third or fourth equation, where I

recommend that you start with the fourth.

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Self-critique (if necessary):

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Self-critique Rating:OK

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Question: Check out the link flow_diagrams and give a synopsis

of what you see there.

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Your solution:

A detailed explanation of how to move forward and backward in a

flow diagram in order to solve a problem.

confidence rating #$&*: 3

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Given Solution: You should have seen a detailed explanation of a

flow diagram, an