Suppose two worlds, each having mass M and radius R, coalesce into a single world. Due to gravitational contraction, the What is the average density of the combined world as a multiple of po, the average combined world has a radius of only R. R. density of the original two worlds?

Please help. This problem involves finding the radius and volume of a platinum atom using its density. Thank you.

There is relatively little space between atoms in solids and liquids, so that the average density of an atom is about the same as matter on a macroscopic scale - approximately 10^3 kg/m^3. The nucleus of an atom has a radius of about 10^-5m of that of the entire atom, and conatins nearly all mass of the atom.  a) What is the approximate density, in kilograms per cubic meter, of a nucleus.  b) One possible remnant of a supernova, called a neutron star, can have the density of a nucleus, while being the size of a small city. What would be the raduis, in kilometers, of the neutron star with a mass 10 times that of the Sun? The radius of the Sun is 7*10^8 m and its mass is 1.99*10^30 kg

For this problem, we want to estimate the answer, so our assumptions may be a little unrealistic. Suppose we want to estimate how much air we need to send to a space station, assuming we cannot recycle air. Suppose four astronauts are in a spherical space station. If each of them typically breathes about 500 cm³of air with each breathe, and take 15 breathes per minute (average resting value): a. What is the volume of air you would need in the space station if these four astronauts stayed for a full year? b. If the density of air is 1.25 kg/m³ and it costs (thanks to SpaceX) a mere $100/kg to send objects to the space station, how much money would the astronaut air supply cost?