Assume that the average galaxy contains 1011 msun and that the average distance between galaxies is 10 million light-years. calculate the average density of matter (mass per unit volume) in galaxies. what fraction is this of the critical density we calculated in the chapter?

Estimate the kinetic energy of mars with respect to the sun as the sum of two terms, that due to its daily rotation about its axis, and that due to its yearly revolution about the sun. (assume mars is a uniform sphere with mass = 6.4×10 to the power of 23 kg, radius = 3.4×10 to the power of 6 m, rotation period = 24.7 hours, orbital period = 686 days and is 2.3×10 to the power of 8 km from the sun.)