4 QA questions

course phy 201

9/21 around 3:30 am

You should submit at least the first four questions of this document, in the same manner as the preliminary qa problems you submitted before. The process is straightforward:•Give your solution.

• Read the given solution.

• If necessary self-critique by demonstrating what you didn’t previously understand but now know after reading the given solution, and what you still aren’t sure you understand.

• If you are unsure of the question-answer-self-critique process, see the notes at the end of this document for further explanation.

• In any case, the process is fairly self-explanatory.

It shouldn’t take you more than a few minutes to work through the first four questions.

You might find it worth your time to complete the rest.

002. Velocity

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Question: `q001. Note that there are 14 questions in this assignment.

If an object moves 12 meters in 4 seconds, then at what average rate is the object moving? Explain how you obtained your result in terms of commonsense images.

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Your solution:

3 meters/sec

simply divide distance traveled 12, by seconds it took 4

confidence rating: very confident

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Given Solution:

Moving 12 meters in 4 seconds, we move an average of 3 meters every second.

We can imagine dividing up the 12 meters into four equal parts, one for each second. Each part will span 3 meters, corresponding to the distance moved in 1 second, on the average.

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Self-critique (if necessary):

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Self-critique rating:

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Question: `q002. How is the preceding problem related to the concept of a rate?

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Your solution:

It is the average rate of speed traveled over a given interval. Meaning the rate of change in distance over change in clock time. This is the definition of avg velocity.

confidence rating: confident, I believe this is what you were getting at with the question asked

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Given Solution:

A rate is obtained by dividing the change in a quantity by the change in another quantity on which is dependent. In this case we divided the change in position by the time during which that change occurred.

More specifically

• The rate of change of A with respect to B is defined to be the quantity (change in A) / (change in B).

An object which moves 12 meters in 3 seconds changes its position by 12 meter during a change in clock time of 3 seconds. So the question implies

• Change in position = 12 meters

• Change in clock time = 3 seconds

When we divide the 12 meters by the 3 seconds we are therefore dividing (change in position) by (change in clock time). In terms of the definition of rate of change:

• the change in position is the change in A, so position is the A quantity.

• the change in clock time is the change in B, so clock time is the B quantity.

So

(12 meters) / (3 seconds) is

(change in position) / (change in clock time) which is the same as

average rate of change of position with respect to clock time.

Thus

• average velocity is average rate of change of position with respect to clock time.

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Self-critique (if necessary):

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Self-critique rating:

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Question: `q003. Is object position dependent on time or is time dependent on object position?

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Your solution: position is dependant on time

confidence rating: very confident

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Given Solution:

Object position is dependent on time--the clock runs whether the object is moving or not so time is independent of position. Clock time is pretty much independent of anything else (this might not be so at the most fundamental level, but for the moment, unless you have good reason to do otherwise, this should be your convention).

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Self-critique (if necessary):

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Self-critique rating:

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Question: `q004. So the rate here is the average rate at which position is changing with respect to clock time. Explain what concepts, if any, you missed in your explanations.

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Your solution:

I believe I covered it all

confidence rating: confident

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Given Solution:

Be sure you have reviewed all the definitions and concepts associated with velocity. If there’s anything you don’t understand, be sure to address it in your self-critique.

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Self-critique (if necessary):

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Self-critique rating:

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&#Very good responses. Let me know if you have questions. &#