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Latest 25 Comments  0  Click here to jump to the problem!  OptimusPrime
20170408 04:47:54  This is really helpful! The point of fastest velocity of the rope shaking happens when crossing the yaxis, which is maximum E amplitude in this case. 
1  Click here to jump to the problem!  OptimusPrime
20170408 02:27:42  (A) and (B) are maybes so far.\r\n(C)  No, we are dealing with PROTONS instead of the usual electrons. So the mass of the electron shouldn\'t come into play at all.\r\n(D)  Maybe.\r\n(E)  No, since after this collision the photon must lose energy. Recall that higher frequency means higher energy. So if we are losing energy, that means our frequency has decreased, and since frequency and wavelength are inversely related, the wavelength has increased. \r\n\r\nIf you remember the Compton equation then you\'ll find as Yosun wrote that change in wavelength equals the Compton wavelength. But, where can we extract any numbers from that?! We can\'t, so (A) and (B) are out.\r\n\r\nThat leaves (D). On top of that, (D) has the correct dimensions. [h/mc] = (M*(L^2) / T) / (M*L / T) = L. Length as in wavelength. 
2  Click here to jump to the problem!  OptimusPrime
20170408 00:55:51  I\'m confused. Choice (E) resembles the function y = which has positive concavity, not negative like the graph shows. 
3  Click here to jump to the problem!  OptimusPrime
20170408 00:36:49  For (B), plugging in = 90 degrees gives 90/2 = 45 degrees. Then, cos(45) = . It also has the correct dimensions. How else do we eliminate (B)? 
4  Click here to jump to the problem!  liuyuhang599
20170404 14:43:16  Your answer is correct, gives two possible states ( +>  +>) the singlet state, and ( +> ++> ) the triplet state. And because electron is fermion, only the antisymmetric singlet state is allowed. 
6  Click here to jump to the problem!  dipanshugupta
20170331 10:12:40  Here \\\'s my method, using \\makebf{Picking Numbers}. Pick a time, say 12, because it is divisible both by 24 and 36. In 12 mins, \\alpha decays \\frac{1}{4} and \\beta decays \\frac{1}{6} . Add them up to get \\frac{5}{12} , which is close to half. Take a time little more than 12. Hence, 14.4 minutes. Pick C. 
8  Click here to jump to the problem!  dipanshugupta
20170330 07:35:09  If you have ever studied the Harmonic Oscillator, you\'ll know that and are Creation and Annihilation operators, i.e, they increase or decrease one quanta of Energy. \r\nI. The commutator gives one negative quanta of energy. \r\nII. Wrong if III is correct. \r\nIII. Definitely, as per above discussion. \r\n\r\nThus, answer is C. \r\n\r\n(I have taken a QFT class so it was easier for me but it\'s in QM too). 
11  Click here to jump to the problem!  dipanshugupta
20170329 10:02:01  Simpler answer. Beta Decay is a Weak Interaction. Weak Interactions are Parity Violating. Parity is a Reflection invariance as . Hence, problem solved. 
13  Click here to jump to the problem!  NervousWreck
20170328 17:21:16  The most straitforward is to draw a PV diagram where an adiabatic expansion would be a curve, which is steeper than an isoterm. Therefore one immediately notices that the E is False. 
17  Click here to jump to the problem!  NervousWreck
20170328 09:45:40  This is a very complicated problem due to the lack of time. However the fasters solution as I see it is the following\r\n. Here rate is 2, which is multiplied by 1%. On the LHS is an error of poissson distribution with 2 measurements per second taken into account. The solution gives N = 5000, which now corresponds to seconds. 
20  Click here to jump to the problem!  blabla0001
20170325 09:26:30  this solution is too good for me. it is also so good that it becomes dangerous. hope i ll never need it again 
23  Click here to jump to the problem!  NoPhysicist4
20170323 14:53:40  Do not mix infinite square well and harmonic potential as I did. In the first case, the numbering starts from 1, while the latter employs 0 as the initial state. Therefore the correct answer is E. 




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