Homework 7
Due: Thursday, 23rd May
Chapter 22
Show your work when required!
2. A typical white dwarf has a mass of 1Msun and a radius similar to that of the earth (6,000,000m in radius). A neutron star created during a supernova has a mass of about 1Msun and a radius of 15 km.
a) Calculate the density of the white dwarf in kg m^{-3}. (Hint conversion of solar mass to kg) (2 marks)
b) Calculate the density of the neutron star in kg m^{-3}. (Hint how many m in a km?)(2 marks)
c) How much mass would a box of neutron star that is 400m on a side have(2 marks)?
d) How does this compare with mass of the earth(1 mark)?
3. a) Describe one piece of evidence for why Einstein's theory of general relativity was accepted over Newton's laws (see the boxes in Chapter 22)(2 marks).
b) Describe one piece of observational evidence for Black Holes (see the book)(2 marks).
4. The angular momentum of a spherical object is given by L = 2/5mwr^2 where m is the mass, r the radius, L the angular momentum and w the angular speed.
a) A star with mass 1M_sun and a radius of 10,000km rotates round once per day. This star then turns into a pulsar, angular momentum and mass are both conserved (they stay the same) but the radius decreases to 10km. How many times per day does the pulsar rotate? (2 marks)
b) How many seconds does each revolution take if there are 60x60x24 = 86400s in a day.(2 marks)
Total 21 marks