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Phy 133 – Assignment 14: A. 1. Mesons have integer spin, while baryons have half-integer spin. Another possible answer is that baryons tend to be heavier than mesons. 2. For each particle, substitute its quark composition from the formula sheet. (a) u d uud ds uds has a total of 1 up, 2 down and 0 strange quarks, both before and after. (b) ud uud us uus has a total of 3 up, 0 down, and 0 strange quarks, both before and after. (c) u s uud us ds sss has a total of 1 up, 1 down, and 1 strange quark, both before and after. (d) uud uud ds uud ud ? has a total of 4 up, 2 down and 0 strange quarks before. Assuming no weak interaction takes place, these numbers must be conserved as they were in parts a – c. The first three particles right of the arrow have a total of 3 up, 1 down, and -1 strange quarks. That leaves an u, d and s unaccounted for. From the formula sheet, uds is a 0. B. 1. It is radiation which formed in the big bang, and has filled the Universe ever since. (It has moved freely through space since the matter, such as hydrogen, became transparent a few hundred thousand years after the big bang.) 2. v = HR where H (.16)(3 x 108 m/s) = (.022) R R = 4.8 x 107 / .022 = .022 m/s light year 2.18 x 109 ly 3. C. (a) Can’t. Violates conservation of baryon number: (b) Ok. Charge = +2 both before and after. Baryon number = +2 both before and after. All lepton numbers = 0 both before and after. (c) Can’t. Violates conservation of electric charge. Total charge = +2 before and +3 after. (d) Violates conservation of baryon number: (e) Ok. (f) Ok. (g) Can’t. Violates conservation of baryon number and μ lepton number. D. 1. There are several answers: The most fundamental difference is that hadrons feel the strong force, leptons don’t. Another is that hadrons are heavier than leptons. Or, hadrons have measurable diameters while leptons appear to be pointlike. Or, hadrons are much more numerous. (There are hundreds of hadrons, but only six leptons.) 2. 3. E. 1. Use x components to find time needed to cross elevator: x = vxt x = ct t = x/c Then, use y components to find vertical distance moved in that time: y = viyt + ½ ayt2 (When giving this quiz, I’ll have a PHY 131 formula sheet with me in case you have trouble remembering that.) y = 0 + ½ (-g)t2 (Which direction is positive is your choice. I wanted y to come out negative because the spot on the wall moves down.) y = - ½ g (x/c)2 2. The principle of equivalence says being accelerated is the same thing as being in a gravitational field. Part 2 of the question is equivalent to part 1, and therefore has the same answer. 3. y = - ½ g (x/c)2 = = 6.67 x 10-6 So, tan θ = 6.67 x 10-6 At small angles, tan θ = θ, so 6.67 x 10-6 rad (Or if you prefer it in seconds, multiply by 180/π and by 3600.)