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Questions, practice, etc

By Minormajor (Minormajor) on Friday, October 01, 2004 - 10:06 am: Edit

My son took the AP physics exam last spring. His teacher had always provided the formulas for all the tests in class and did not mention that the students should have them memorized. Big mistake...my son managed a 3 and Physics is one of his best subjects. Other kids in his class had the same problem.

By Legendofmax (Legendofmax) on Saturday, October 02, 2004 - 02:08 am: Edit

No Physics questions?

By Joshjmgs (Joshjmgs) on Saturday, October 02, 2004 - 11:51 am: Edit

If anyone hasn't bought review books for the November sitting:

GOOD Books: Kaplan and Princeton Review (I'm using PR this time 'round)

OK, but not reccomended: Barrons

BAD: Sparknotes

By Legendofmax (Legendofmax) on Saturday, October 02, 2004 - 01:05 pm: Edit

I'm going with PR this time as well.

By Collegebound123 (Collegebound123) on Saturday, October 02, 2004 - 01:12 pm: Edit

What's wrong with Barrons?

By Samwise (Samwise) on Saturday, October 02, 2004 - 07:52 pm: Edit

Are sparknotes tests bad as well?
I'm taking the test next saturday and have been using them to prepare. Are they much easier than the real thing?

By Thermodude (Thermodude) on Saturday, October 02, 2004 - 08:10 pm: Edit

Here's a Physics question I just thought up:

A object with a mass of 1 kg travels along a frictionless surface with a velocity of 10 m/s. It then travels over a rough surface, where the coefficient of friction between the object and ground is Uk = 0.50. How many seconds will it take for the object to stop? (Note to use 10 m/s^2 for g)

By Lolboyer (Lolboyer) on Sunday, October 03, 2004 - 01:00 pm: Edit

5 seconds? is that the answer?

By Legendofmax (Legendofmax) on Sunday, October 03, 2004 - 02:46 pm: Edit

10 N for the weight... the Friction force would be 10 N * .50 or 5N... so if the velocity is 10 m/s, the KE = (1/2)(1)(100) or 50J, or 10m for a distance...

10 m = Vavg*time, where Vavg = (10 + 0) / 2 or 5

10 m = 5 m/s * time

time = 2 seconds?

By Thermodude (Thermodude) on Sunday, October 03, 2004 - 05:28 pm: Edit

Legendofmax has it correct....the answer should be indeed 2 seconds.

Here's another question I just thought up:

A gas is in a fixed sized container and its temperature is 35 celsius. What is its new temperature if the pressure acting on the gas is reduced in half?

By Jaredthegreat (Jaredthegreat) on Sunday, October 03, 2004 - 05:48 pm: Edit

(1/2)mv^2=µk*mg*x
50kg*m^2/s^2=5kg*m/s^2*x
10m=x

?x=(V^2-Vo^2)/2a
a=(V^2-Vo^2)/2x
a=(0-100m^2/s^2)/20m/s^2
a=-5m/s^2

V=at+Vo
t=(V-Vo)/a
t=-10(m/s)/-5(m/s^2)
t=2s

By Korinfox (Korinfox) on Sunday, October 03, 2004 - 05:53 pm: Edit

wow thats quite a bit of calculations.... since mu=.5 deceleration is .5*g = 5m/s^2 so 2 seconds
other problem
pressure is halved PV=nRT so temperature is halved
(35+273)/2=154 so.... 154 degrees kelvin or -119 or so degrees celcius?

By Legendofmax (Legendofmax) on Sunday, October 03, 2004 - 06:34 pm: Edit

I'm gonna say 17.5 degrees...

P1 / T1 = P2 / T2

Ummm so for grins I am gonna use 2 for P1.

2/(35 + 273)K = 1/T2

(35 + 273)K/2 = 308K / 2 = T2

154K = T2

154K - 273 = T2 = -119 degrees Celsius

By Thermodude (Thermodude) on Sunday, October 03, 2004 - 08:42 pm: Edit

154 Kelvin or -119 Celsius is the correct answer for the gas problem...

..i'd have to say that Korinfox probably has the best methods of solving problems for the SAT II Physics...it always helps to use simple calculations so that you can finish more quickly.

By Korinfox (Korinfox) on Sunday, October 03, 2004 - 10:11 pm: Edit

^^ happy to help out, took the SAT II Physics last may, and the AP Physics C exams too
if there are any more questions I'll be happy to entertain them...

By Legendofmax (Legendofmax) on Sunday, October 03, 2004 - 10:29 pm: Edit

What are some interesting facts you know about light and sound?

By Korinfox (Korinfox) on Sunday, October 03, 2004 - 10:38 pm: Edit

haha... I meant AP or SAT II type problems but I'll try...
well, there is that whole thing about light and wave particle duality thingy and of course the fact that it has momentum but not mass or anything
what else... light has an interesting property of bouncing off surfaces at all sort of angles (see Feynman's sum over histories theory) not just the angle which allows for the sace angle of incidence and reflection...
sound, well the funny thing is that 10 times the amount of sound (1 person talking vs. 10 people talking) which is an increase of 10 on the decibel scale (which is logarithmic which makes sense) but that 10 decibel increase is perceived as twice as loud (funny eh?)
also I think, a sound at 90 decibels (OHSA standard) you can listen for 8 hours, 95 decibels 4 hours, 100 db 2 hours and so on and so one without risk of hearing damage, (at 120 db a "rock cocert" that makes what... 7.5 minutes?)
I dunno what else I can think of now, I'm not exactly taking any physics classes this year (took at the ones my high school offers and at the local univ. 9-10 mon-fri with a 45 minute commute isn't too doable...)
Are you impressed? (ha a physics teacher quote)

By Legendofmax (Legendofmax) on Sunday, October 03, 2004 - 10:56 pm: Edit

LOL my physics teacher always says that too.

By Legendofmax (Legendofmax) on Monday, October 04, 2004 - 09:35 pm: Edit

When is the velocity of a block attached to a horizontal spring greatest after compressing the spring and releasing it?

By Korinfox (Korinfox) on Monday, October 04, 2004 - 09:42 pm: Edit

Well if you think about it hard enough.... think about it this way, you know acceleration is greatest when the spring is fully compressed (or extended) because of the spring's F=kx (Hook's) equation right? so when would the velocity be greatest?

By Legendofmax (Legendofmax) on Monday, October 04, 2004 - 09:54 pm: Edit

The velocity is fastest halfway between the two oscillation points

By Korinfox (Korinfox) on Monday, October 04, 2004 - 11:00 pm: Edit

yup! or at the equilibrium point, which is the term usually used...

By Legendofmax (Legendofmax) on Monday, October 04, 2004 - 11:07 pm: Edit

Any other questions you know of?

By Legendofmax (Legendofmax) on Monday, October 04, 2004 - 11:07 pm: Edit

Any other questions you know of?

By Thermodude (Thermodude) on Tuesday, October 05, 2004 - 12:19 am: Edit

Just for a notice, there are quite a few circuit questions on the SAT II Physics test (I'd guess maybe 4 or 5). I'd definately review Ohm's law and that stuff, as well as the resistance of R in series, and parrerel, as well as the capatence of Capacitors in series and parrerel.

By Legendofmax (Legendofmax) on Tuesday, October 05, 2004 - 01:18 am: Edit

To those who have taken the test, which topics need studying in-depth and which concepts are a bit more obscure (but still appear on the test)?

By Legendofmax (Legendofmax) on Tuesday, October 05, 2004 - 09:06 am: Edit

Bump?

By Midwesterner (Midwesterner) on Tuesday, October 05, 2004 - 09:27 am: Edit

Does anyone know if there are any questions on Modern Physics on the SATII?

By Joshjmgs (Joshjmgs) on Tuesday, October 05, 2004 - 12:03 pm: Edit

Midwesterner, yes Modern Physics is included on the test. You have to know:
-the photoelectric effect and its graph
-special relativity and graph of kinetic energy
-nuclear physics (not too in-depth, just how each side of a chemical equation has to have the same amount of electrons, neutrons, and protons, how to calculate half-lifes, what the basic nuclear particles are and their nomenclature, and binding energy)
-rutherford's experiment
-bohr's model of the atom
-wave-particle duality (de Broglie wavelength)

If you are not using a study guide, you can get most of the information about these topics on wikipedia.com

By Legendofmax (Legendofmax) on Tuesday, October 05, 2004 - 06:46 pm: Edit

Can anyone explain various "important facts/equations" pertaining to electric/magnetic fields?

By Legendofmax (Legendofmax) on Tuesday, October 05, 2004 - 08:51 pm: Edit

Ok I'll start? Electric field lines go away from a positive source, but they go towards a negative source.

By Legendofmax (Legendofmax) on Tuesday, October 05, 2004 - 11:57 pm: Edit

... does no one care about this test? lol

By Joshjmgs (Joshjmgs) on Wednesday, October 06, 2004 - 10:08 am: Edit

F = kqQ/r^2
E = KQ/r^2 = F/q
F = Eq = ma
Work = Kinetic Energy = F*d =kQq/r
Change in position requires energy, which equals kQq/r2 - kQq/r2 = kQq(1/r1-1/r2)
V = -W/q = U/q = -(kQq/r)/q = -kQ/r

Anything I am missing?

By Midwesterner (Midwesterner) on Wednesday, October 06, 2004 - 10:42 am: Edit

Thank you, Joshjmgs.

One more question: Are the numeric values for constants (such as Planck's) given on the test, or must they be memorized?

By Conker (Conker) on Wednesday, October 06, 2004 - 11:01 am: Edit

They would never ask you to know any constants. The only one I would even consider memorizing is g = 9.81 m/s^2 (or 10), but I think they even tell you that on the test. Otherwise, you aren't expected to know any constants.

By Collegebound123 (Collegebound123) on Wednesday, October 06, 2004 - 12:02 pm: Edit

This came from Sparknotes but I don't understand the explanation they gave at all:

(Optics)
3. When the orange light passes from air (n = 1) into glass (n = 1.5), what is its new wavelength?
(A) 4 x 10^-7 m
(B) 4 x 10^-6 m
(C) 2.5 x 10^-7 m
(D) 6 x 10^-7 m
(E) 9 x 10^-7 m

The answer they gave was (A).

I understand that frequency does not change when passing from one material to another. So wavelength changes and so doe speed.

By Collegebound123 (Collegebound123) on Wednesday, October 06, 2004 - 12:05 pm: Edit

Another question: Is Sparknotes way easier than the real test? It seems like some of the questions are too easy (plug it into the equation type questions).

By Joshjmgs (Joshjmgs) on Wednesday, October 06, 2004 - 05:49 pm: Edit

Sparknotes' tests are DIFFERENT from the real one.

Orange light's original wavelength is ~6E-7 meters long. And its velocity through glass is 1.5 = c/v => v = c/1.5 = 2E8 meters/second.
We can calculate orange light's frequency => c/(6E-7) = 5E14
As you said, frequency does not change, but the measureent of speed and wavelength do.
Wavelength = v/f = (2E8)/(5E14) = 4*10^-7 meters
Your Answer is A

On the real test, I think you will be given that Orange light's frequency is 10^14 or its wavelngth is ~6*10^-7

By Legendofmax (Legendofmax) on Wednesday, October 06, 2004 - 09:03 pm: Edit

How about facts pertaining to light now?

By Collegebound123 (Collegebound123) on Wednesday, October 06, 2004 - 09:12 pm: Edit

How is Sparknotes' tests different from the real one? (Aside from the obvious: different questions) Elaborate please. Does it relate to the difficulty? Type of questions? Number of questions from each category (kinematics, optics, etc.)?

By Legendofmax (Legendofmax) on Wednesday, October 06, 2004 - 09:45 pm: Edit

The real thing seems difficult. I was reading the past Physics threads on this site. There's a lot about electric fields, light, magnetism, and thermal physics I don't know yet (like putting objects of blabla degrees C into water of blabla degrees C), or specific heat thingies.

By Legendofmax (Legendofmax) on Wednesday, October 06, 2004 - 11:04 pm: Edit

Anyone willing to discuss Physics over AIM?

By Legendofmax (Legendofmax) on Thursday, October 07, 2004 - 02:17 am: Edit

I give up. LOL.

By Conker (Conker) on Thursday, October 07, 2004 - 11:05 am: Edit

Are there numerous mistakes on Sparknotes? I'm not even going to count the numerous instances in which the explanations refer to the answer as (B) but the answer is listed as (A). I could be wrong, so if you would, please correct me.

Dynamics
10. The correct answer is C, but shouldn't it be instead: (u_k)mg <= F < (u_s)mg. They have the less than/equal signs mixed around.

Special Problems in Mechanics
7. This problem fails to mention that the spring is vertical and not horizontal, although if it were the type of spring described in (6), none of the given choices would be correct.

Linear Momentum
7. This seems to be the worst mistake of all. None of the choices are correct. If you look at their explanation, the "two-body system" clearly refers to post-collision. However, they use m as the mass instead of 2m, when calculating kinetic energy. I could be wrong on this one, and if I am, I would appreciate being corrected.

By Joshjmgs (Joshjmgs) on Thursday, October 07, 2004 - 12:19 pm: Edit

I just typed up a long answer to Collegebound's question and then my computer shut down, so I am abbreviating my answer.

Sparknotes does not test how well you know the information in the book, just the equations. On the real test you have to know how to apply those equations to word problems, graphs, modern physics, conceptual questions concerning gravity and centripital force, field direction, complex circuits, the laws of thermodynamics, interference patterns...

There are a number of conceptual questions where the equations you memorized are useless! It is very important that you know the conceptual physics very well. And Sparknotes does not help here.

I studied using Sparknotes, I practically memorized the book (I just happen to have a good memory, so after reading it four times or so, it just stuck) and I didn't feel prepared. I don't think Princeton Review teaches the conceptual information as well as it could, but it covers as the basics and anyone can extrapolate information from what is presented, and its modern physics section is more concise and the author is clearer than Barnes and Noble is.

By Legendofmax (Legendofmax) on Thursday, October 07, 2004 - 06:44 pm: Edit

Princeton Review seems nice so far but it seems like there isn't enough concept. Anyone know of useful concepts?

By Legendofmax (Legendofmax) on Saturday, October 09, 2004 - 09:21 am: Edit

How was it, guys?

By Perfectdark9 (Perfectdark9) on Saturday, October 09, 2004 - 09:30 am: Edit

I used Barron's and got a 790. :S