Which of these are not mechanical waves and can be used to send a signal to astronauts on the moon?

a) sound waves
b) radio waves
c) both sound waves and radio waves
d) neither sound waves or radio waves

Under normal conditions, describe how increasing the temperatures effects the solubility of a typical salt

Often called simply "velocity," this is the velocity of an object at a particular moment in time.

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?