<p>its been 48 hrs... the frq are now up on collegeboard.com :<a href="http://apcentral.collegeboard.com/apc/public/repository/ap08_physics_b_frq.pdf%5B/url%5D">http://apcentral.collegeboard.com/apc/public/repository/ap08_physics_b_frq.pdf</a></p>
<p>so what did you guys get? or any questions?</p>
<p>1.
a. 3.6 seconds
b. i. 1.16 m/s
ii. right
c. no, kinetic energy isnt conserved </p>
<p>2.
a. F = 0.8 N
b. x = 0.01 m
c. same
d. greater (used math for c and d)
e. x = 0.177 m</p>
<ol>
<li><p>a. L = 0.721 m
b. up
c. B = 0.75 T
d. a straight line from the origin with a less steep slope (a line below the original)
e. Didnt know</p></li>
<li><p>a. v = 2.23 m/s
b. flow rate = 1.12 x 10^-4 m^3
c. pressure = 3.16 x 10^4 N/m^2</p></li>
<li><p>a. Wasnt sure, but definitly W=0 for a->b
b.
c. V = 0.005 m^3</p></li>
<li><p>a. One ray is parallel and then through the focal point, one is through focal point and then parallel
b. real, image is on same side of mirror as object
c. di = 24 cm
d. smaller, I drew 2 rays for a diverging mirror</p></li>
</ol>
<p>7.
a. p = 1.75 x 10^-23 kgm/s
b. Dont think I did the rest right, I used KE= hf-work function, but it might have just been KE = 1/2mv^2
c.
d.</p>
<p>i'm so mad about #2.. my teacher did them today, and i realized i didn't take into account the entire system when drawing my force diagrams and finding the acceleration.. i only did the mass that the forse was on... so my answers are all off.. so i got the answer to (a) wrong... (b) was based on my (a) answer, and i did that right, so i got those points.. (c) is wrong for me.. my (d) is right.. and my (e) is right some how because i got what you got.. x = .177</p>
<p>so you think i can get 8 to 9 points on that one (out of 15)? i showed all of my equations first.. i hope so.. that happened to me on a practice test i took at home, and i managed to get a 9/15 just by doing that.. i also made a 2/15 on another FR and still made a 5 on that exam too, so i guess i shouldn't worry too much about one mistake</p>
<p>the KE = hf - work function was used on the last part (d).. on b it was just p = mv (p is known, m is 9.11 x 10^-31) and v is the one needed.. (c) was just KE = .5mv^2.. and (d) was the work function one</p>
<p>on 3(a) it gave the internal resistance, so i used emf = IR - Ir (or I(R -r)) and found R.. then i used that in R = pl/A (i think that's the equation) and solved for l.. i got what you got, so i assume that's the right way to do that</p>
<p>and on the last part of that problem, i didn't know what kind of experimental error there could have been..i said there could have been another source of a magnetic field that the student didn't account for, resulting in the discrepencies.. i didn't know what to say lol</p>
<p>yay! got all of them right except the last one</p>
<p>i got all of them right except for some of #2 (the easy one........ lol)</p>
<p>how did you calculate number 1 part a?</p>
<p>i can't remember my answer but if i see the method i might know if i did it right</p>
<p>First you find distance traveled such that 5 m/s is reached. Use vf = v + at, where v=2, vf=5, a=1.5 to find time, then use x = vt + 1/2at^2 to find distance, i think its 7 m traveled. </p>
<p>Which means that out of the 15 m, there is still 8 m to travel at 5 m/s with a=0 (constant velocity). So then use x = vt + 1/2at^2 to see the time traveled for 8 m, but a = 0 so 8 = (5)(t), t=1.6 s, but you add that to the time traveled before to reach 5 m/s, which was 2 s. So 2 + 1.6 = 3.6 s.</p>
<p>somehow i blanked on 4b (VERY easy) and 4c, both stuff we didn't do in class but that I could use the equations, didn't know how to do 5, and gave a subpar explanation for 6b (lol: the image is inverted and all inverted images are real). other than that I think i got just about all the points. Would that be a 5 worthy FR?</p>
<p>for 3e I put that once the power supply is turned on, the wire will begin to heat (due to power dissipated which i didn't exactly say) up, causing the current to decrease, which would cause a concave down graph like that.</p>
<p>all i know is i got 6 completely right
everything else is such a blur</p>
<p>mike, you had to solve a quadratic right? because i got a little concerned when i had to do that ( never did a question where i needed to do that before)</p>
<p>I think i got it though... (hopefully)</p>
<p>Not for the part I described. I remember starting to factor a quadratic on one of the problems but I ended up not having to...it might have been the water fountain one, finding the velocity.</p>
<p>uhhh shoot.</p>
<p>i did a quadratic for number 1 part a</p>
<p>sigh....</p>
<p>^^ i think i remember it looking like a quadratic but i just punched it into my calculator...</p>
<p>yea i punched my quadratic into my calculator</p>
<p>For the A to B process on # 5 i got W = 0, Q +, dU +</p>
<p>W = 0 because work is equal to the area under the curve. no area under a verticle line so its 0.</p>
<p>Q i said + and my reasoning was that for the pressure to increase while the volume remained constant, heat had to be added to the system. Basically i got that from PV = nRT</p>
<p>and then for dU i got + because dU = Q + W and a positive + zero will be positive.</p>
<p>As for the rest of the chart i kept getting distracted as i filled it out so i don't remember what i put and at this point i doubt if it was right. however, how does my reasoning sound for 5b?</p>
<p>oh and for 3b, i put upward but i remember BS'ing my reasoning. basically i guessed and then wrote down that it was due to the direction of the current through the wire/right hand rule for the magnetic field that was produced. will i get any credit there?</p>
<p>Inital velocity of car A is 5 m/s, not 2 m/s, it has already accelerated to 5 by the time it hits car b. And it tells you car b's final velocity is 4.8....did you miss that?</p>
<p>ma(va inital) + mb(vb inital) = ma(va final) + mb(vb final)
250(5) + 200(0) = 250(v) + 200(4.8)</p>
<p>no I didn't forget I put that in. nvm.</p>
<p>are you sure that for 3(a), your answer is correct? i dont exactly remember but i think i got something like .9</p>
<p>and for 3(b), can you explain why its up?</p>