Physics tends to naturally organize itself in terms of concepts and classes (types) of problems. The midterm is designed to emphasize the most important concepts and problems from the material we have covered so far, (emphasizing what we have covered in class) and to test your understanding of that. Here is an outline of what to expect:
1) Conservation of energy is important. Review energy conservation principles and understand how to do problems related to that. Understand the idea of an abstracted potential energy (P.E.) curve. For example, for a mass in a gravitational field P.E. = m g y, where y is height, and for a mass attached to a spring P.E. = (1/2) k x^2 .
Be able to graph a potential energy curve, like the above, and to understand motion under the influence of a potential energy. (There is an example of a problem involving motion under the influence of a P.E. in the earlier midterm post.) This is important.
2) Review the concept of center of mass. Be able to calculate tension on ropes supporting a scaffold. Understand the value of symmetry in such problems. Be able to solve rope-tension problems in symmetric and non-symmetric situations. Understand how to recognize and exploit symmetry, which is a key concept.
3) The idea that overall macroscopic quantities can be related to microscopic (atomic scale) phenomena is a important part of physics. Review temperature and understand its relationship to molecular motion. Understand/appreciate the advantages of the Kelvin temperature scale. How is it aligned to make it more fundamentally meaningful than other temperature scales?
Understand how to do problems, like those of the HW and quiz, where you compare speeds of thermal molecules which have differing masses or you figure out how speed changes with temperature or visa versa. Understand how to do this quickly via scaling ideas, e.g., if you double T, how much does v change? If a molecule is 4 times heavier how much slower would it have to go to have the same kinetic energy?...
4) Matter is made of atoms, which are very small. The atomic picture of matter is important. In preparation for the midterm familiarize yourself with the composition and size (atomic radius) of the following relatively light atoms: H, D, He, Li, C, O, Ne .
You should know which has the largest size (atomic radius) and which has the smallest size (atomic radius). Most of the others have roughly the same size, so don't worry about the details of that, but make sure you do know roughly the size of the largest one*, to one significant figure is sufficient (i think it is either 0.2 or 0.3 nm), and also be sure you understand what a nanometer is. (What does it have to do with the number 1 billion?) [ *I think it is Li, but you should probably look that up.]
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Will we need a scantron or blue book for the midterm?
ReplyDeletewill hw #3 solutions be posted any time today?
ReplyDeleteFor the question "If a molecule is 4 times heavier how much slower would it have to go to have the same kinetic energy?..." how would you figure that out?
ReplyDeletehw #3 solutions are online, two posts below this one (along with quiz #2 solutions)
ReplyDeleteK.E. = (1/2)*m*v^2
v(old) = SqRoot(2*KE/m)
if m becomes 4m,
v(new) = SqRoot(2*KE/4m) = SqRoot(1/4)*v(old)=(1/2)*v(old)
so, the molecule would have to go half as slow.
Will there be anything else to this post?
ReplyDeleteI just want to know if this is all we need to review for the midterm
Are we going to be given the formulas? if not, which ones do we need to memorize?
ReplyDeletehow good are the quizzes for preparation?
ReplyDeletequizzes are great for preparation -- the ideas behind the questions are more important than the number crunching.
ReplyDeleteequations to know would be potential and kinetic energies, the relationship between temperature and mass/velocity in a gas, the relationship between frequency and fundamental frequency...
I don't want to tell you that's everything you'll need, but it should be at the top of your list.
Hopefully Zack will check this tonight, as only he can give the final word.
also, will we really be asked to compute the numerical value of a component vector, or should we just know the principle behind what happens with uneven tension in ropes?
ReplyDeleteYou won't be given any formulas. What I believe is most essential is familiarity with the content, meaning and implications of the relationship between kinetic energy, mass and speed.
ReplyDeleteAlso, for a mass on a plank type problem, use g = 10 (kg m/s^2).
I really don't think you would need to memorize anything else. Hopefully you are familiar with all the above concepts though.
no resolving of vector components.
ReplyDelete"...make sure you do know roughly the size of the largest one*, to one significant figure is sufficient (i think it is either 0.2 or 0.3 nm), and also be sure you understand what a nanometer is" how do we figure this out
ReplyDeleteThe midterm review did not include all components that were needed to take the test smoothly. The was no mention that we needed to know the individual proton and neutron quantities of elements, and the questions (Number 5 for the most part) needed to be worded more carefully so that we are able to create pictures and diagrams. I felt that the midterm did not cover the course material enough and more time time should be taken when composing study guides.
ReplyDeleteHi, will we be getting our midterms back soon, I found #5 to be really confusing as well and therefor am a little worried
ReplyDeleteJason,
ReplyDeleteI appreciate your comment, however, it does say above (in the “Midterm Study Guide” that: “In preparation for the midterm familiarize yourself with the composition and size (atomic radius) of the following relatively light atoms: H, D, He, Li, C, O, Ne . “
I am not sure how you were interpreting “composition” in this context. I has intended it to refer to the number of protons, neutrons and electrons.
I agree that #5 was difficult. I spent a lot of time thinking about the wording of this one, but I am open to suggestions regarding how to word that better. You were asked to prepare for this sort of problem in the post on Midterm Content and Study Advice” which said:
“…there will be a question regarding masses moving in a potential energy… Familiarize yourself with the 1/2 k x^2 potential…” and “Understand how to work problems involving potential energy. For example:
Suppose a mass, m, is subject to a force such that its potential energy as a function of x is (1/2) k x^2 (like if it were attached to a spring...). a) Where is the lowest point of this potential? b) graph this potential as a function of x. c) suppose the mass starts out at the lowest point of the potential with an initial speed of v (to the right). What will happen? How far will it go before its speed decreases to zero? What will happen after that? Assume there is no friction.”
[i think anyone who did that would be prepared?]
Also in the study guide it said:
“Understand the idea of an abstracted potential energy (P.E.) curve. For example, for a mass in a gravitational field P.E. = m g y, where y is height, and for a mass attached to a spring P.E. = (1/2) k x^2 .
Be able to graph a potential energy curve, like the above, and to understand motion under the influence of a potential energy. (There is an example of a problem involving motion under the influence of a P.E. in the earlier midterm post.) This is important.”
We will get the midterms back as soon as we can. Maybe Friday, maybe Monday. Don't want you to worry any longer than necessary.
Actually the thing that surprised me was that no one posted any online questions before the midterm related the mass moving-in-a-potential problem (which became #5).