A point charge Q moves on the x-axis in the positive direction with a speed of 370 m/s. A point P is on the y-axis at y = +80 mm. The magnetic field produced at point P, as the charge moves through the origin, is equal to 0.80x10^6 T in the NEGATIVE z direction . When the charge is at x = +40 mm, what is the magnitude of the magnetic field at point P?

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?