<p>I think because the graph was a subquestion of the differential equation question, it was inferred that the time interval was when the block was being acted upon by the braking force.</p>
<p>^Right, which is why I said it was implied. I did not catch that the first time around when I did the problem on the exam, but now rereading the question, it makes sense why they’d be referring only from D to E.</p>
<p>Would it still have a asymptote because A=kv/m and v is a exponential function and it’s not zero till t= infinity</p>
<p>^But we can’t have the cart not ever stop, since it’s a roller coaster.</p>
<p>Copied from the other Physics C thread are my answers:</p>
<p>My procedure/thought process for #1 Mech:</p>
<p>For (a) and (b), v is v_x</p>
<p>(a) J=Ft, so t=J/F
(b) J=mv, so m=J/v
(c) Work done in stopping the projectile is the change in kinetic energy. KE=.5mv^2, so it’s .5(J/v)v^2, which is .5Jv
(d) Work is equal to average force times distance. So .5Jv=Fd. So F_b=.5Jv/d
(e)/(f) I know that the impulse imparted by the projectile on the block is equal to something, which I wrote on the test for both parts. Hopefully I get points.</p>
<p>Same for #2 Mech:</p>
<p>(a) 2 forces, normal and gravity. Gravity straight down, Normal perpendicular to surface
(b) Screwed this one up, said Mgcos(theta). Maybe I’ll get something for writing normal=centripetal?
(c) Conservation of energy from point A (all gravity potential) to point D (all kinetic). h for mgh is 7R/4.
(d) I only remember getting 7/12 for my coefficient of friction. Which might not even be what I put. 
(e) i. -kv=m(dv/dt)
ii. Integrate
iii. Initial acceleration (i.e. at point D) is kv/m (even though I only put v). Concave up, decreasing, horz. asy. of acceleration equals 0.</p>
<p>For Mech. #3 (a=alpha, B=beta, O=theta):</p>
<p>(a) Ia=-BO. Replace a with double derivative of theta with respect to time and divide I over.
(b) Using small angle approximation, alpha=-(angular velocity)^2 times theta. Angular velocity is sqrt(B/I). Period=2pi/angular velocity. Could also use mass on spring analogy, with m=I and k=B.
(c) Graph.
(d) My slope was like 160, y-int .20. y=160x+.2 or T^2=160I+.2
(e) Checked my calculator, got .247. Units are same as that of spring constant.
(f) No clue.</p>
<p>well it can rest at t= infinity the problem said nothing about a finite time and no real amusement park ride functions like that</p>
<p>^ for 1d, i used kinematics, using v^2 = Vx^2 -2ad
2ad = Vx^2 , i solved for a and put it in f = ma. is that right?</p>
<p>do you think for Mech FRQ 3, F, the discrepancy with the intercept is caused by friction??? </p>
<p>It would make sense since it says “physical significance” but I really don’t know for sure.</p>
<p>@Etennis: That’s what I did for 1d, and it is correct.</p>
<p>shouldn’t the work done for 1c be negative given the change in KE is negative?</p>
<p>^I had negative work, but I don’t think they’re going to care.</p>
<p>i just realized i messed up on 1b which affected c and d. i first wrote J=delta p = mv, but then for some dumb reason that only a power greater than myself could comprehend, i wrote m=v/j as my final answer, which then obviously changed c to .5v^3/J and d as .5v^3/Jd. Think they’ll take off a point each time? I know that it would be error carried forward, but if there is a point awarded for having the right answer, even though error was carried forward, I didn’t actually have the correct answer.</p>
<p>They don’t double jeopardize in the grading so if your answer affected succeeding parts they will ignore the mistake in the preceding parts.</p>
<p>^Agreed. If you use a wrong answer from (c) correctly in (d) (or wrong answer in (b) correctly in (c)), you’ll get full points for the section in which the wrong answer was used correctly.</p>
<p>^So, as long as the reasoning/method behind each part of a problem is correct, full points will be awarded even if I got an earlier part incorrect?</p>
<p>Like even if I said the coefficient of friction came out to be 50,000 and if the method was correct, I would get credit? (this is just a hypotehtical case, I didn’t actually get u=50,000). I’m sure there must be some kind of a limit on absurd answers.</p>
<p>If the braking force is proportional to the velocity, the cart will never completely stop…</p>
<p>^I know, which confused me as to whether or not the graph of acceleration ever hits 0.</p>
<p>^I just made it asymptotically approach zero because there was no specified time interval.</p>
<p>^Same here. </p>
<p>Hehe, think of a roller coaster that never ever stops.</p>
<p><thanks for=“” that.=“” i=“” do=“” too.=“” had=“” not=“” my=“” medical=“” issues=“” in=“” the=“” first=“” semester=“” when=“” applied=“” to=“” oxford=“” (and=“” hence=“” couldn’t=“” study=“” at=“” all=“” entrance=“” exam),=“” perhaps=“” would=“” have=“” gotten=“” a=“” conditional=“” offer=“” there=“” as=“” well.=“” reapplied=“” this=“” year=“” after=“” having=“” missed=“” deadline,=“” but=“” don’t=“” mind=“” way.=“” much=“” prefer=“” london,=“” family=“” is=“” 45=“” minutes=“” away=“” by=“” car.=“” question,=“” yeah,=“” that=“” same=“” errie=“” feeling.=“” and=“” think=“” third=“” part.=“” also=“” thought=“” it=“” was=“” two=“” easy,=“” were=“” ways=“” of=“” doing=“” both=“” gave=“” me=“” answer=“” so=“” went=“” with=“” it.=“” last=“” parts=“” though,=“” physically,=“” made=“” no=“” sense=“” because=“” sentence.=“” got=“” some=“” very=“” strange=“” constant=“” integral=“” though=“” on=“” q=“” 2.=“”></thanks></p>
<p>Silonthesofa,</p>
<p>Goodluck with your 5! Which course did you apply for Imperial? They want another 5 in addition to your 16 AP’s!!! Are they ok with Calc AB or do they insist on Calc BC also? Are unconditional offers ever possible? </p>
<p>Do do they consider SAT subject test scores - that is if you have 800 for example in SAT physics, does that fulfill the Physics requirement in place of AP when its a 4 instead of a 5? What are the general requirements in terms of GPA / Transcript etc. Heard UK admission is mainly focussed on AP scores only. Is it correct?</p>
<p>Is interview mandatory there? Did you come under international applicant category ?</p>
<p>[Applications</a> and Offers](<a href=“Imperial College London”>Imperial College London) states “we do not interview majority of applicants” and hence was not sure?</p>
<p>any idea if Oxford insists on Calc BC and Physics C or if they are ok with Calc AB and Physics B for Math/Science majors?</p>
<p>@query123</p>
<p>i applied for theoretical physics at Imperial. yes, they want a 5 because due to health issues, I wasn’t in school for my first six months of senior year hence I missed mech in school and had to self study in addition with 8 other APs and scored a 4 instead of a 5. that’s in addition to having already scored 5s on physics B, physics C e and m, calc AB, and calc BC. they don’t really consider the SAT for anything, i scored 2300 with an 800 in math, 790 on my physics, didn’t matter. they don’t care much about gpa either, it’s ALL about test scores, specifically your APs. interview is mandatory, I applied last year but couldn’t show up for the interview on account of living in LA, was rejected. Had to convince them to give me the interview this year and they agreed on the condition i get the 5. I believe BC and phys C are mandatory, or else there would be no basis for the 5 on the phys C stipulation since I already have a 5 on B. Yes I applied as an international applicant because even though I’m a UK resident, I don’t have citizen status yet. oxford will definitely want calc BC and phys C as well, with 5s on them. forget your other APs, they don’t matter… at all. had I known, i wouldn’t have bothered with my 16, would have just taken math and physics. Hope my answer helped. feel free to ask any more questions.</p>