If you decrease the charge on a parallel-plate capacitor from 12 µC to 4 µC and increase the plate separation from 1 mm to 3 mm, the energy stored in the capacitor changes by a factor of

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?

Which statement best explains why the overall charge on an atom is zero?

Which system of units is used by only a small number of countries in the world, including the u. s.