5. In class we developed a VERY crude estimate for critical mass: Merit=mu/(n2 03) a. Show that this can be rewritten as M =m,3/(p2 03) where p is the mass density (mass/volume). The mass density of U is approximately 19 g/cm3 and the mass of a 235U nucleus is approximately 3.9 x 102z g. b. Give a crude estimate for the critical mass assuming that the typical cross section for fission in the chain reaction is approximately 50 b. c. Give a crude estimate for the critical mass assuming that the typical cross section for fission in the chain reaction is approximately10b. d. Give a crude estimate for the critical mass assuming that the typical cross section for fission in the chain reaction is approximately 250b. e. Why are the results of b. c. & d. so different given the fact that the cross section in c. is only 5 times smaller than b. and the cross section in d. is only 5 times larger