1.49 White Dwarfs and Neutron Stars. Recall that density is mass divided by volu

Question

1.49 White Dwarfs and Neutron Stars. Recall that density is mass divided by volume, and consult Appendix B as needed. (a) Calculate the average density of the earth in g/cm3, assuming our planet is a perfect sphere. (b) In about 5 billion years, at the end of its lifetime, our sun will end up as a white dwarf that about the same mass as it does now but is reduced to about 15,000 km in diameter. What will be its density at that stage? (c) A neutron star is the remnant of certain supernovae (explosions of giant stars). Typically, neutron stars are about 20 km in diame- ter and have about the same mass as our sun. What is a typical neutron star density in g/cm3?

Explanation / Answer

1.49)
a) density of the Earth = Me/Ve

= Me/(4/3*pi*Re^3)

= 5.98*10^24/(4/3*pi*(6370*10^3)^3)

= 5523 kg/m^3

b) density of the Sun = Ms/Vs

= Ms/(4/3*pi*Rs^3)

= 1.99*10^30/(4/3*pi*(7500*10^3)^3)

= 1.126*10^9 kg/m^3

c) density of A netron star = Mn/Vn

= Mn/(4/3*pi*Rn^3)

= 1.99*10^30/(4/3*pi*(10*10^3)^3)

= 4.75*10^17 kg/m^3

1.57) It depends on our mass.

no of atoms present = mass of our body/ mass of single atom

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