<p>Is a=Aw^2 a shortcut that should be memorized? When can it be applied?</p>
<p>Oh. So the speed we solved for was only the angular speed then, since it’s moving in a circle?</p>
<p>theRADtomato47,</p>
<p>You have to take the derivative of the given expression, which will give you dtheta/dt. (That’s angular velocity.) Then you plug in t=4. Then you have to multiply by the radius to get the speed. (Remember v = r * angular velocity).</p>
<p>For 3.d) i.
<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>Why is it not KE + U = 1/2kx^2?
(It says KE = 1/2kx^2 + U.)</p>
<hr>
<p>If a particle moves in a plane so that its position is described by the functions
x = A cos t and y = A sin t, the particle is:
(A) moving with constant speed along a circle
(B) moving with varying speed along a circle
(C) moving with constant acceleration along a straight line
(D) moving along a parabola
(E) oscillating back and forth along a straight line</p>
<p>Why isn’t it E? Aren’t those the equations for a spring?
It’s A.</p>
<hr>
<p>The sum of all the external forces on a system of particles is zero. Which of the
following must be true of the system?
(A) The total mechanical energy is constant.
(B) The total potential energy is constant.
(C) The total kinetic energy is constant.
(D) The total linear momentum is constant.
(E) It is in static equilibrium.</p>
<p>It’s D, I thought it was E?</p>
<hr>
<p>The ring and the disk shown above have identical masses, radii, and velocities, and
are not attached to each other. If the ring and the disk each roll without slipping up
an inclined plane, how will the distances that they move up the plane before coming
to rest compare?
(A) The ring will move farther than will the disk.
(B) The disk will move farther than will the ring.</p>
<p>Doesn’t a ring have more inertia? Doesn’t that mean the ring won’t go as far up, and thus it would be B? The answer is A.</p>
<p>How comparable are the 1998, 1993, and the tests in the 80s to current tests? ALso, is this tests real [AP</a> Physics C Mechanics Practice Tests_°Ù¶ÈÎÄ¿â](<a href=“http://wenku.baidu.com/view/4869e4d6195f312b3169a570.html?]AP”>AP Physics C Mechanics Practice Tests - 百度文库) Cause it seems to be harder than the mentioned ones.</p>
<p>EVERYONE… its not that hard</p>
<p>[AP</a> Physics C Score Calculator](<a href=“http://www.free-test-online.com/ap/ap_physicsc_score.html]AP”>http://www.free-test-online.com/ap/ap_physicsc_score.html)</p>
<p>Abrayo- MC1. those equations should just make you think of the unit circle (ie. let A=1 and you just have your unit circle). It’s not E because it can’t be moving in a straight line if x and y are both varying with time (ie not = 0)</p>
<p>MC2. Static equilibrium implies the system is not moving…an object can move at constant velocity while all forces act on it add up to 0. Linear momentum can only change if there is a net force on the system.</p>
<p>MC3. Assuming both shapes begin ascending the plane at the same velocity, the ring has more kinetic energy (.5Iw^2), so it will reach a higher height (mgh).</p>
<p>PS. for any questions like the first one you posted that you get, it helps to just either mentally plot some points (using easy angles like 0, 45, 90) or draw it out. Usually it should be evident from the plotting what’s going on in the situation.</p>
<p>Hmm, why does the ring have more kinetic energy though? Doesn’t it weigh less because it isn’t solid?</p>
<p>@Rdakker:
It doesn’t seem right to me. It says I can get 22/35 on MC and a 4/4/4 and still get a 4!</p>
<p>Its one of the most rigorous AP tests and has a very low pass rate. Plus the Fr’s are curved. I find it believable, I hope its true</p>
<p><a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>If you put in my hypothetical case of 22, 4/4/4 I would get a low 4.</p>
<p>The ring and the disk shown above have identical masses, radii, and velocities, and
are not attached to each other. If the ring and the disk each roll without slipping up
an inclined plane, how will the distances that they move up the plane before coming </p>
<hr>
<p>Both shapes have the same linear kinetic energy (.5mv^2), but the ring has more rotational kinetic energy (.5Iw^2), so the ring will have more gravitational potential at its highest point.</p>
<p>I’m sorry, I just don’t understand why the ring would have more rotational kinetic energy?
If it’s .5Iw^2, what would it be for the disk?</p>
<p>Now we can all breathe a bit easier knowing that we can get low scores on mc or fr</p>
<p>It’s .5Iw^2 for both shapes; however, I (moment of inertia) is based on the geometric distribution of mass. I of a hoop is MR^2 while I of a disc is .5MR^2. The hoop has more rotational inertia because its mass is concentrated farther away radially from the center.</p>
<p>Ohh I get it! Thank you very much for your patience & explanations!</p>
<p>how is magnetic field related to the rate of change of electric field?</p>
<p>@salzahrah: if you have pr look at page 325. this is demonstrated by the Amepere-Maxwell Law</p>
<p>Does this test really matter if I plan to take the class in college anyway since I have not really learned anything this year due to a bad teacher and senioritis :(?</p>
<p>I was wondering about that too when I saw that problem, salzahrah. The only relation I could come up with is that V=-d(flux)/dt when calculating induced voltages due to changing magnetic fields. Since V is proportional to E and d(flux)/dt is proportional to B, I guess B is proportional to dE/dt?</p>
<p>For those doubting that the curve can be so low, I assure you that it really is that low. In the past, it has typically been 50/90 total points for mechanics for a 5 and 53/90 for EM. In other words, you can flunk the test and still get a 5. It is the lowest curve I know of on the AP tests. 34% of those who take EM get a 5, and more than 60% get a 4 or better. More than 50% get a 4 or better on mechanics, and that is lower simply because more kids take it (not all courses teach EM, and mechanics is typically taken first). When you feel like you’re failing, you probably are, but don’t sweat it too much. </p>
<p>Just remember for tomorrow: Go quickly on the MC. Don’t get stuck on a single problem. This is stuff you all know, but you need to make a conscious effort to do this. Time yourself on some practice exams if you haven’t already. </p>
<p>As for the written section, always write something down. Even if you only have a general idea, write down related formulas. If you are using conservation of energy or conservation of anything for that matter, make it known! Annotate if you have time and make it easy for the reader to see what you are trying to do. Also, if part B requires you to use the answer from part A, that doesn’t mean part A needs to be right to get points on part B. Even if you have no idea how to do A, act like you do. Write down an answer for A and plug that answer in as you solve B. The college board explicitly states that unless the answer to A is incredibly obvious, you will get full credit for B (assuming, of course, that B is correct). Be explicit and points will be forthcoming.</p>
<p>Whew. I’m ready.</p>
<p>I hope.</p>