<p>@smanjotpal - i am dead sure it was chord and not string. Even the answer key posted 2-3 pages back says that :)</p>
<p>That’s not a real answer key because the test was never released, it’s just what people on that thread believe was the correct answer.
Whoever two posts said I was wrong, I’m not because I said W.</p>
<p>Yea, what did you guys say for the loss of heat? smallest area and lowest temp and thickest one?
Also, the tension one is 2W. The diagram had two masses hanging on a pulley with one rope on each side, balanced. Then the pulley was attached to the ceiling by some rope. The question asked the tension of the rope that connects pulley (not masses) and ceiling. Fnet of this string = Fg-Ft, and Fg=Ft since Fnet=0. Fg=2W=Ft. So tension of the rope connecting pulley and ceiling is 2W.</p>
<p>the answer to the question related loss of heat is E? the very last option</p>
<p>The loss of heat was D or E. I don’t remember exactly.
@william22 : we had to calculate minimum loss of heat??? or maximum?</p>
<p>i dont remember if it was max or min… i think min… mine was the one out of the ones with 17C lol…</p>
<p>me too,the 17C one
I think it was D</p>
<p>Definitely struggled with this test haha. My school only offers mechanics classes, so I had to self-teach myself everything else from a book. Omitted 17. Hopefully there is a generous curve.</p>
<p>I did B for the heat loss one. It asked for the minimum heat loss.</p>
<p>By H=m.c.deltaT
the minimum temperature difference was where temperature was 17 degrees.
since all walls had same material (given in question) mass is proportional to volume (density is constant)
since volume = area x thickness,
the wall with minimum product of area x thickness and lowest temperature difference was the answer which was B</p>
<p>@iamthebist : the formula we needed to use was ΔH=(k<em>A</em>(T-t))d where k is a constant,A is the area,d is the thickness, (T-t) difference in temperature.
It is the formula for rate of exchange of heat due to conduction.
<a href=“http://en.wikipedia.org/wiki/Conduction_(heat[/url])”>http://en.wikipedia.org/wiki/Conduction_(heat)</a></p>
<p>How about the capacitator graph? what graph did u guys choose? i chose the one where it has negative slope then zero slope… How is answer negative decay graph?</p>
<p>i think i remember the last question on the test.
it went something like this:
what is the tension in the rope that’s holding the elevator when it moves down with acceleration 2m/s^2 .
mass of elevator = 1000kg</p>
<p>i think the answer should have been 8000 N
correct me if im wrong. i used the following logic:
since the elevator is moving down, the tension in the rope will be upwards.
hence we can set up an equation: </p>
<p>mg - T = ma
or T = m(g-a)
= 1000(10-2)
= 8000 N</p>
<p>what do you guys think?</p>
<p>it is indeed 8000 N :)</p>
<p>^ Was that choice (E)? Does anybody remember?</p>
<p>Hang on… I distinctly remember that the problem said the acceleration was downwards. So my equation was set up like this: T = mg + ma, since the tension would be counteracting both the force of the downward acceleration and the weight of the elevator. So I think my final answer was 12000 N. I don’t understand what’s wrong with this reasoning…</p>
<p>EDIT: Never mind. This equation would only apply in the situation where the elevator was accelerating upwards. Bleh… that leaves me with 2 wrong. What would a raw score of 56 yield? Hopefully it’s still above 750…</p>
<p>WAIT! (Heh… sorry for being a pest.) According to this website, my answer was correct:</p>
<p>[Tension</a> in an elevator cable- Physics problem and solution](<a href=“Strona główna | Uniwersytet im. Adama Mickiewicza w Poznaniu”>http://www.staff.amu.edu.pl/~romangoc/M3-P5-elevator-cable-tension.html)</p>
<p>It seems that in the case where the acceleration is pointed downwards, T = m(g + a) is the correct equation to use… now I’m just confused. LOL.</p>
<p>@calgirl: Tension in this case is upwards. So if it had been 12000N the elevator would have been going upwards instead of downwards.</p>
<p>OK… but I thought the upward tension was supposed to counteract both the weight of the elevator (mg) and the force of the acceleration (ma). Plus, the website I linked said this situation would call for mg + ma, and it doesn’t seem like a random site with potentially incorrect facts (I just checked, and the site is maintained by a physics professor at a Polish university).</p>
<p>In the question on the site you mentioned, the elevator is slowing down ie. the acceleration is upwards. So Tension(upwards)-Weight(downwards)=ma(upwards) ma=force of retardation
Therefore T-mg=ma and T=mg+ma</p>
<p>In the question on the physics test, the elevator is speeding up ie. acceleration is downwards. So Weight(downwards)-Tension(upwards)=ma(downwards) ma=force of acceleration
Therefore mg-T=ma and T=mg-ma</p>
<p>Oh, I see. Thanks! At least I’ve learned something new today. 
Now I just hope a raw score of 56 will still yield at least a 750… :/</p>