query 7 

course phy 231

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007. `query 7

Physics I

02-07-2008

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19:28:26

Describe the flow diagram you would use for the uniform acceleration situation in which you are given v0, vf, and `dt.

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RESPONSE -->

each would have its own seperate line. the average velocity is found using the initial and final velocity.

then velocty over time to find acceleration

confidence assessment: 2

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19:28:44

Describe the flow diagram you would use for the uniform acceleration situation in which you are given `dt, a, v0

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RESPONSE -->

confidence assessment:

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19:30:43

Explain in detail how the flow diagram for the situation in which v0, vf and `dt are known gives us the two most fundamental equations of motion.

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RESPONSE -->

ave and dt = ds

final velocity is found using the initian velocity.

acceleration and time = velocity

confidence assessment: 2

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19:30:56

**Student Solution:

v0 and vf give you `dv = vf - v0 and vAve = (vf + v0) / 2.

`dv is divided by `dt to give accel. So we have a = (vf - v0) / `dt.

Rearranging this we have a `dt = vf - v0, which rearranges again to give vf = v0 + a `dt.

This is the second equation of motion.

vAve is multiplied by `dt to give `ds. So we have `ds = (vf + v0) / 2 * `dt.

This is the first equation of motion

Acceleration is found by dividing the change in velocity by the change in time. v0 is the starting velocity, if it is from rest it is 0. Change in time is the ending beginning time subtracted by the ending time. **

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RESPONSE -->

self critique assessment: 0

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19:34:46

qaExplain in detail how the flow diagram for the situation in which v0, a and `dt are known gives us the third fundamental equations of motion.

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RESPONSE -->

vf = v0 + dv = v0 + a dt

2 is then divided by both sides of the equation

vAve = vf + v0 /2 = v0 + v0 + a dt / 2 = v0 + 1 /2 a dt

the average velocity and the change in velocity is used in the acceleration of motion

self critique assessment: 0

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19:37:48

Accelerating down an incline through a given distance vs. accelerating for a given time

Why does a given change in initial velocity result in the same change in final velocity when we accelerated down a constant incline for the same time, but not when we accelerated down the same incline for a constant distance?

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RESPONSE -->

change in velocity is based on distance.

the greater the distance, the greater the velocity

confidence assessment: 3

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19:37:54

** If we accelerate down a constant incline our rate of change of velocity is the same whatever our initial velocity.

So the change in velocity is determined only by how long we spend coasting on the incline. Greater `dt, greater `dv.

If you travel the same distance but start with a greater speed there is less time for the acceleration to have its effect and therefore the change in velocity will be less.

You might also think back to that introductory problem set about the car on the incline and the lamppost. Greater initial velocity results in greater average velocity and hence less time on the incline, which gives less time for the car to accelerate. **

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RESPONSE -->

self critique assessment: 0

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