Assignment2-1

course Phy 231

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001. `Query 1

Physics I

09-10-2007

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17:04:42

Briefly state what you think velocity is and how you think it is an example of a rate.

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RESPONSE -->

Velocity is the change in speed and direction of an object. It's an example of a rate because velocity is the rate of change of position over clock time.

confidence assessment: 3

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17:04:55

** A rate is a change in something divided by a change in something else.

This question concerns velocity, which is the rate of change of position: change in position divided by change in clock time. **

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RESPONSE -->

OK

self critique assessment: 2

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17:05:50

Given average speed and time interval how do you find distance moved?

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RESPONSE -->

You multiply the average speed by the time interval to get the distance moved.

This is just canceling out units.

5m/s * 10s = 50m

confidence assessment: 3

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17:06:01

** You multiply average speed * time interval to find distance moved.

For example, 50 miles / hour * 3 hours = 150 miles. **

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RESPONSE -->

OK

self critique assessment: 2

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17:07:17

Given average speed and distance moved how do you find the corresponding time interval?

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RESPONSE -->

You divide the average speed by the distance to cancel out the distance units.

This is a cancellation of units problems as well.

5m/s * 1/10m = 0.5s

confidence assessment: 3

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17:07:47

** time interval = distance / average speed. For example if we travel 100 miles at 50 mph it takes 2 hours--we divide the distance by the speed.

In symbols, if `ds = vAve * `dt then `dt = `ds/vAve.

Also note that (cm/s ) / s = cm/s^2, not sec, whereas cm / (cm/s) = cm * s / cm = s, as appropriate in a calculation of `dt. **

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RESPONSE -->

OK

self critique assessment: 2

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17:08:40

Given time interval and distance moved how do you get average speed?

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RESPONSE -->

average speed = distance moved / time interval.

Average speed is often given in units of m/s

so for example if an object moves 10m in 5s then you get:

10m/5s = 2m/s

confidence assessment: 2

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17:08:50

** Average speed = distance / change in clock time. This is the definition of average speed.

For example if we travel 300 miles in 5 hours we have been traveling at an average speed of 300 miles / 5 hours = 60 miles / hour. **

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RESPONSE -->

OK

self critique assessment: 2

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"

Very good.

Note that units calculations are necessary; if the units don't work out then something is amiss. However units calculations are not sufficient; for example the units of vAve / `dt are the same as the units of `dv / `dt, but only one of these calculations (the latter) has any physical significance.