Assume biological substances are 90 percent water and the density of water is 1.0 ✕ 103 kg/m3.

(a) estimate the mass of a spherical cell with a diameter of 2.50 µm (volume = 4/3 π r3)

(b) estimate the mass of a fly, which can be approximated by a cylinder 3.40 mm long by 1.70 mm in diameter (volume = l π r2)

answers should be in kg

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?