cq_1_161

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Phy 201

Your 'cq_1_16.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.

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Seed Question 16-1 Revision

The purpose and the process of answering 'seed' questions:

In cloud seeding small crystalline particles (the 'seeds') are scattered throughout a cloud, so that water vapor in the cloud will build up on the 'seed' and eventually fall in the form of rain.

These questions are posed without any previous explanation. You are expected to use what you already know, along with common sense, to answer the questions. It is standard practice in many courses to an instructor to give explanations and examples before asking students to answer questions, and you will see plenty of examples and explanations in this course. However the goal here is to first experience and think about a situation. Whether you think correctly or incorrectly, your thinking gets you started on an idea and forms a 'seed' on which understanding can accumulate.

• You are expected to answer it to the best of your ability, based on what you know at the beginning of this assignment.

• You are not expected to research this question until after you have submitted your best response.

• You are not penalized based on whether your answer is 'right' or 'wrong', but you are expected to think as clearly and deeply as you can about the question.

• You are not, however, expected to spend hours thinking about the question or agonize unduly about your answers. A rule of thumb is to give it up to 20 minutes, half for thinking and half for typing in your answers (maybe a little more for the typing if you don't have good keyboard skills).

• Your answers should consist of your best attempt at a solution, and/or one or more questions about the situation.

• If you think you know the answer or can make a reasonable attempt to answer, then give your answer along with a concise outline of your reasoning.

• If you aren't sure what the question is asking, make your best attempt to interpret and answer it, and consider including one or more questions.

• If you are very sure you don't know what the question is asking, then break it down phrase-by-phrase or even word-by-word and explain what you think each key phrase or word might mean.

• A question consists of a complete but concise statement of what you do and do not understand about the situation.

• There are two ways you can spend an excessive amount of time explaining your solutions and/or asking questions. One is to type a lot more than what is necessary, and another is to spend a lot of time worrying about what is and is not necessary. Balance the two in the way that works best for you.

• Remember that the 'concise' part is more for your benefit than mine. I can read a lot more quickly than you can type, and don't mind reading through a lot of words to understand your meaning.

• You are invited but not required to include comments and/or discussion.

• You are welcome to use reasonable abbreviations in your work.

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Copy the problem below into a text editor or word processor.

• This form accepts only text so a text editor such as Notepad is fine.

• You might prefer for your own reasons to use a word processor (for example the formatting features might help you organize your answer and explanations), but note that formatting will be lost when you submit your work through the form.

• If you use a word processor avoid using special characters or symbols, which would require more of your time to create and will not be represented correctly by the form.

• As you will see within the first few assignments, there is an easily-learned keyboard-based shorthand that doesn't look quite as pretty as word-processor symbols, but which gets the job done much more efficiently.

You should enter your answers using the text editor or word processor. You will then copy-and-paste it into the box below, and submit.

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A rubber band has no tension until it reaches a length of 7.5 cm. Beyond that length its tension increases by .7 Newtons for every additional centimeter of length.

• What will be its tension if its endpoints are at the points (5 cm, 9 cm) and (10 cm, 17 cm) as measured on an x-y coordinate system?

answer/question/discussion: ->->->->->->->->->->->-> :

Using a distance formula I found, sqrt((x2-x1)^2 +(y2-y1)^2), The distance of the rubber band is Sqrt(89) or about 9.43.

Therefore the tension would be about .7N*1.93cm = 1.4N

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Good.

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• What is the vector from the first point to the second?

answer/question/discussion: ->->->->->->->->->->->-> :

The vector would be 9.43cm

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A vector has a magnitude and a direction.

It can be specified by its magnitude and direction or by its components.

In this case it should be clear that the x component is 5 cm and the y component 8 cm. So the vector could be specified as

<5 cm, 8 cm>.

Alternatively it could be specified as 9.43 cm, at angle arcTan(8/5).

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• What is the magnitude of this vector?

answer/question/discussion: ->->->->->->->->->->->-> :

I don’t understand what the difference between the vector and the magnitude of the vector is.

The magnitude should be 9.43cm by my calculation.

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• What vector do you get when you divide this vector by its magnitude? (Specify the x and y components of the resulting vector).

answer/question/discussion: ->->->->->->->->->->->-> :

If I divide the vector 9.43 by the magnitude 9.43 it is 1.

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That is the magnitude of the vector.

When you divide a vector by a positive number, its direction isn't changed (were you to divide it by a negative number its direction would reverse).

So the vector has magnitude 1, at angle arcTan(8/5).

You would be better off for this series of questions finding the components of this vector. The easiest way to do this is to divide the component form

<5 cm, 8 cm>

by the magnitude 9.43 cm.

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• The new vector should have magnitude 1. When you divide a vector by its magnitude the result is a vector with magnitude 1. We call a vector of magnitude 1 a unit vector. What vector do you get when you multiply this new vector (i.e., the unit vector) by the tension?

answer/question/discussion: ->->->->->->->->->->->-> :

I’m still lost but 1unit vector*1.4N = 1.4

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Had you divided the component form of the vector by its magnitude, you would have obtained a vector of magnitude 1 in the direction of the original vector. Your vector would have been in component form.

We you to then mutliply the resulting component form of the magnitude-1 vector by 1.4 N, you would obtain the component form of the new vector, which would be the force vector.

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• What are the x and y components of the new vector?

answer/question/discussion: ->->->->->->->->->->->-> :

I have no idea

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You're making good progress, but you're missing the fact that a vector has a direction, and also the useful fact that a vector can be specified by giving its components.

See my notes and see if you can take this a couple of steps further.

&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).

Be sure to include the entire document, including my notes.

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