1. [-/1 Points] DETAILS OSCOLPHYS2016 34.1.P.001. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Find the approximate mass in kg of the luminous matter in the Milky Way galaxy, given it has approximately 104 stars of average mass 1.4 times that of our Sun. kg Additional Materials Reading 2. [-/1 Points] DETAILS OSCOLPHYS2016 34.1.P.002. MY NOTES ASK YOUR TEACHER Find the approximate mass in kg of the dark and luminous matter in the Milky Way galaxy. Assume the luminous matter is due to approximately 10 stars of average mass 1.5 times that of our sun, and take the dark matter to be 10 times as massive as the luminous. kg Additional Materials Reading 3. [-/1 Points] DETAILS OSCOLPHYS2016 34.1.P.004. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER If a galaxy is 800 Mly away from us, how fast do we expect it to be moving in km/s and in what direction? velocity km/s direction --Direction--4. [-/1 Points] OSCOLPHYSZO16 34.1.P.006. ASK YOUR TEACHER Our solar system orbits the center of the Milky Way galaxy. Assuming a circular orbit 30000 ly in radius and an orbital speed of 250 km/s, how many years does it take for one revolution? Note that this is approximate, assuming constant speed and circular orbit, but it is representative of the time for our system and local stars to make one revolution around the galaxy. yr Additional Mat-rials El Reading 5. [-/1 Points] OSCOLPHYSZO16 34.1.P.007. ASK YOUR TEACHER PRACTICE ANOTHER (a) What is the approximate speed in km/s relative to us of a galaxy near the edge of the known universe, some 13 Gly away? (Use 20 km/s - Mly for the Hubble constant.) km/s (b) What fraction of the speed of light is this? Note that we have observed galaxies moving away from us at greater than 0.9c. c 6. [-/1 Points] DETAILS OSCOLPHYSZO16 34.2.P.022. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER What is the Schwarzschild radius in km of a black hole that has a mass eight times that of our Sun? Note that stars must be more massive than the Sun to form black holes as a result ofa supernova. km Additional Materials El Reading 7. [-/1 Points] DETAILS OSCOLPHYSZMG 34.2.P.023. MY NOTES ASK YOUR TEACHER Black holes with masses smaller than those formed in supernovas may have been created in the Big Bang. Calculate the radius (in m) of one that has a mass equal to the Earth's. m Additional Materials Ell Reading 8. [/1 Points] DETAILS OSCOLPHYSZO16 34.2.P.024. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Supermassive black holes are thought to exist at the center of many galaxies. (a) What is the radius in m of such an object if it has a mass of 1010 Suns? m (b) What is this radius in light years? |Y OSCOLPHYSZO16 34.2.WA.015.TUTORIAL. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER (a) During a supernova, a particular star expels an enormous amount of mass. The remaining stellar remnant has a mass of 1.65 times the mass of the sun, MSun = 1.99 x 1030 kg, and forms a 9. [/1 Points] neutron star. The density of a neutron star is about the same density as an atomic nucleus, or about 4.00 x 1017 kg/m3. What is the radius (in m) of the neutron star? m (b) A second star undergoes a similar supernova, but in this case the remaining stellar remnant is 14.0 times the mass of the sun. Such a large object will collapse to a black hole. Assuming no rotation, what is the radius (in m) of the black hole's event horizon? (That is, the radius where the escape velocity is equal to the speed of light, and below which nothing can escape.) rn Addltlonal Materials m Reading OSCOLPHY52016 34.3.P.026. ASK YOUR TEACHER 10. [/1 Points] The characteristic length of entities in Superstring theory is approximately 10'35 m. (a) Find the energy in GeV ofa photon of this wavelength. GeV (b) Compare this with the average particle energy of 1019 GeV needed for unification of forces. 11. [I1 Points] OSCOLPHYSZO16 34.4.P.027. ASK YOUR TEACHER PRACTICE ANOTHER If the dark matter in the Milky Way were composed entirely of MACHOs (evidence shows it is not), approximately how many would there have to be? Assume the average mass ofa MACHO is 1/1000 that of the Sun, and that dark matter has a mass 10 times that of the luminous Milky Way galaxy with its 1011 stars of average mass 1.4 times the Sun's mass. MACHOS Additional Materials III Reading 12. [-I1 Points] OSCOLPHYSZO16 34.4.P.028. ASK YOUR TEACHER PRACTICE ANOTHER The critical mass density needed to just halt the expansion of the universe is approximately 10'26 kg/m3. (a) Convert this to eV/c2 - m3. eV/c2 - m3 (b) Find the number of neutrinos per cubic meter needed to close the universe if their average mass is 4 eV/c2 and they have negligible kinetic energies. ASK YOUR TEACHER (a) Find the volume our sun would occupy in m3 if it had an average density equal to the critical density of 10-25 kg/m3 thought necessary to halt the expansion of the universe. 13. [l 1 Points] OSCOLPHY52016 34.4.P.030. To get an idea of how empty deep space is on the average, perform the following calculations. m3 (b) Find the radius of a sphere of this volume in light years. Rgc) = 4 ly (c) What would this radius be in ly If the density were that of luminous matter, which is approximately 5% that of the critical density? Iy (cl) Compare the radius found in part (c) with the 4 ly average separation of stars in the arms of the Milky Way. Additional Malorials III Reading OSCOLPHY5201 6 34.6.WA.022. ASK YOUR TEACHER PRACTICE ANOTHER For it to be economically feasible to use a superconducting wire, the cost to cool the superconducting wire must be less than the cost of energy lost to heat if using an equivalent conduction wire. You have a wire that is super conducting at the temperature of liquid nitrogen. You wish to pass a current of 40.0 A through it and you need 1.60 L of liquid nitrogen per hour to cool the wire. You could instead use an equal length of braided copper wire, which has a resistance of 2.05 n. The cost of electrical energy is $0.10/kw - h. What is the maximum cost (in dollars) per liter of liquid nitrogen you can pay in order to use the superconducting wire before it becomes cheaper just to use the copper wire? $ /L 14. [-/1 Points]