physics  fluid mechanics
posted by cindy .
Neutron stars consist only of neutrons and have unbelievably high densities. A typical mass and radius for a neutron star might be 3.4 multiplied by 1028 kg and 2.0 multiplied by 103 m.
(a) Find the density of such a star.
(b) If a dime (V = 2.0 multiplied by 107m3) were made from this material, how much would it weigh (in pounds)?

(a) density = (Mass)/(Volume)
= [3/(4 pi)]*Mass/(radius)^3
(b) Multiply the density that you get in (a) by the volume of a dime (2*10^7 m^3). That will give you the mass in kg. Multiply that by 2.2 lb/kg for the weight in pounds. (They want you to assume that the dime is on the Earth, with acceleration of gravity 9.8 m/s^2.)
It would be so heavy that it would probably sink to the center of the Earth. You might want to compare the mass of the dime to the mass of the Earth.