<p>can someone explain why 1 and 4 is most current and 2 and 5 is least current? thanks</p>
<p>@UrAverageAzn This problem deals with energy. I don’t see what this has to do with momentum.</p>
<p>i just remembered the superconductor question. when it is cooled below the critical temperature 20K the resistance approaches 0</p>
<p>For the potential energy question, i remember reading at the end of the question that before it hits the ground it was at maximum KE meaning that according to the conservation of energy, the top would have to be max PE? someone let me know if i read that right.</p>
<p>The thermodynamics question with the PV diagram: Why is it that heat and temperature both increase? I mean I used the equation </p>
<p>ΔU=ΔW+ΔQ</p>
<p>I was thinking that since ΔW was negative (since it’s work done ON the system), then if ΔQ is also negative so that heat decreases, then negative+negative would have to be a negative ΔU, so a decrease in Temperature as well. </p>
<p>Then again, I’m really bad at thermodynamics…</p>
<p>oh and for the elastic collision question, can someone explain how it’s 4 m/s?</p>
<p>It deals with the conservation of momentum. So in the beginning, the two objects are moving in one direction, but after the collision, one moves in the other direction, so the total momentum must stay the same, so the larger more massive object moves at 4m/s in the original direction.</p>
<p>Sorry I don’t remember the numbers for the question.</p>
<p>I thought that the volume expanding means that work is being done by the system so that temperature would stay constant even as heat was added. But that wasn’t an option so I said temperature was decreasing because instaneously isn’t that what happens?</p>
<p>Also, does anyone remember the spring scale question? I said .8 because 1 couldn’t possibly be right, could it?</p>
<p>@emmmei</p>
<p>PV=nRT
V=nRT/P</p>
<p>P, n, R are all constant. V increases, therefore T must also increase.</p>
<p>@desafinado</p>
<p>it was 1</p>
<p>@emmmei: You’re right that ∆U=W+Q. Remember that U=3/2nRT=3/2PV. Because ∆(PV)>0, ∆U>0. W<0 as you said since W=-∆(PV). Thus Q>0 (∆U>0, W<0). And T must increase since ∆(PV)>0. So the correct answer is that heat is added and temperature must increase.</p>
<p>@Desafinado: The answer is 1 because the mass of the spring scale is irrelevant. It’s no different from when you hang the scale from a bar vertically.</p>
<p>Wow, looking at the consolidated list of problems, I got like -1. Looks like I’m heading towards an 800 after all!</p>
<p>Ohhhh I see! Thank you! hahah even though I got that one wrong =P</p>
<p>Anyone know that question regarding energy transfer to the outside surroundings? like it was in a cup, but then the cup quadrupled its thickness, then what’s the power?</p>
<p>It was 12W initially</p>
<p>Answer was 3 W.</p>
<p>Q/t=kA∆T/L, so power is inversely proportional to distance the heat is transferred through. 4 times the thickness will result in 1/4 the rate of heat transfer.</p>
<p>So doesn’t that make it 3W? 1/4th of 12.</p>
<p>whoops you’re right, fixed.</p>
<p>what was the answer of that antimatter question?</p>
<p>positron read the thread</p>
<p>@ honeywell
Well momentum is directly proportional velocity, which suggests that the man jumping from the plane would have both potential AND kinetic energy (simply mv^2). This problem has probably already been resolved but yea just wanted to let you know.</p>
<p>Yeah, isn’t the consensus PE>KE?</p>
<p>What did u guys put for the red light?</p>