<p>the windy city is rocking
arena football style
up 2 TD's already</p>
<p>Well, I took a KAP Physics class this year. Not really an official AP, it's based off a course at Kenyon University or something. The point is that it was mainly based around AP Physics C Mechanics. It looks like the SAT Physics test covers the same stuff as AP Physics B.</p>
<p>So, I just started to hit the new stuff. We studied up to oscillations (also did waves and relativity, but that's later). This is really boring, I have to say. It looks like the topic of Physics deteriorates into a bunch of equation-memorization once you leave the interesting stuff (mechanics).</p>
<p>
[quote]
A pendulum with length 1 m has a mass of 1 kg at
the end. The mass has +200 micro-C of charge. An
oppositely charged identical mass sits 10 m
directly below the lowest point of the arc of
the pendulum. What is the period of oscillation?</p>
<p>A) 2.5 sec
B) 1.9 sec
C) 1.8 sec
D) 1.7 sec
E) 1.5 sec
[/quote]
dude...there's NO WAY that can be done with just simple AP Physics B or even AP Physics C stuff. First of all, a pendulum travels in a semi-circle arc, meaning that the distance changes very non-linearly when it gets closer or farther from the charged stationary object. Since the electric field is inversely proportional to this distance, and F=EQ, yes the charged object effectively increases g but different amounts at different times. So unless these thigns somehow cancel out, which may be true considering this happens quite often in problems =), i dont see how you can get an exact answer without some form of advanced math. You can, however, totally estimate =)</p>
<p>^ That's what I was thinking too. Where's the poster to tell his the answer/his reasoning? ^_^</p>
<p>Actually I think it's possible to integrate along the arc. But I forget how, and I don't think enough info was provided lol</p>
<p>So... does anyone know where I can find some challenging practice tests for SAT Physics? I know about the PR book, but I could use more than just two tests. I'm looking for practice tests which will be harder than the real thing.</p>
<p>Barron's is an obvious suggestion, but I would rather use something else because the Barron's Physics book is supposed to have tons of errors.</p>
<p>Sparknotes.</p>
<p>You're making it too hard. Assume the pendulum amplitude is small compared to 10m (it kind of has to be considering that the pendulum length is 1m!).</p>
<p>is the barron's book really that bad? i'm using it right now, and i don't really want to buy another haha</p>
<p>eh yeah u can calculus</p>
<p>and fignewton i LIKE to make things hard! :)</p>
<p>Not only would you need calculus, you would have to be familiar with elliptic integrals to find the "big swing" pendulum period. Hard enough? :)</p>
<p>Hint: Pretend, effectively, that the distance from the lower charge to the upper charge is always 10 m.</p>
<p>Don't make me post a new problem! :)</p>
<p>That sounds like an AP Physics C-type problem.</p>
<p>Umm, are you sure the effective g gets larger considering there is an additional downward acceleration?</p>
<p>I kind of remember that g becomes bigger when an elevator accelerates upward and g is smaller when an elevator accelerates downward.</p>
<p>do i get any formulas? because i don't have any right now, but i know that u find the force by doing f=kqq/r2 and then you divide by teh mass, and then add that to g, and then plug it into the T=2pi rt.l/g equation, to get T</p>
<p>yeah effective G gets larger because gravity is downward, and the mass is also pulled downward because its attracted to the charge</p>
<p>Effective G? I've never heard of it before. It doesn't look like the Princeton Review talks about it either...</p>
<p>It looks like now I have to worry about what PR doesn't cover.</p>
<p>effective G is just acceleration downwards, inthe direction of gravity</p>
<p>That would never be on the SAT II test cuz you have no calculator</p>
<p>I think the test is alittle tight on time but the questions are generally easy. Is it just me?</p>
<p>Why not just call it the effective force, which is the combined gravitational and electric force that points downwards? And then find the acceleration of the effective force? :P</p>
<p>I totally did not see the part in the initial post that it was 10m below. I missed the 10 m and only read "directly below," which is why you can now probably imagine why I gave up - especially considering that the period would be VERY small if it was directly below lol. </p>
<p>Here it is reworked:</p>
<p>For a pendulum, the period T is defined as T = 2pi(L/Atotal)^1/2. The mass is irrelevant.</p>
<p>L = 1 m. Atotal = g + a(electric).</p>
<p>g = 9.8m/s^2, Fe = k(200)^2/r^2 = ma, so a = k(200x10^-6)^2/r^2
since k = 9 x 10^9, r=10 m; we get a = 3.6m/s^2 (hopefully this is right - I don't have my scientific calculator on me)</p>
<p>Atot = 13.4m/s^2</p>
<p>T = 1.7 seconds, so choice D</p>
<p>Why don't we practice types of problems that will actually be on the test instead of problems that OBVIOUSLY won't be?</p>