39, 40. (IT) Four 9.5-kg spheres are located at the corners of a square of side 0.60 m. Calculate the magnitude and direc- tion of the total gravitational force exerted on one sphere by the other three. (IT) Every few hundred years most of the planets line up on the same side of the Sun. Calculate the total force on the Earth due to Venus, Jupiter, and Saturn, assuming all four planets are in a line (Fig. 5-38). The masses are My = 0815Mg. My = 318Mg, Mg = 95.1 Mg, and their mean distances from the Sun are 108, 150, 778, and 1430 million km, respectively. What fraction of the Sun's force on the Earth is this? Sun - - FIGURE 5-38 Problem 40. (Not to scale.) 81. Astronomers using the Hubble Space Telescope deduced the presence of an extremely massive core in the distant galaxy M87, so dense that it could be a black hole (from which no light escapes). They did this by measuring the speed of gas clouds orbiting the core to be 780 km/s at a distance of 60 light-yvears (5.7 X 10" m) from the core. Deduce the mass of the core, and compare it to the mass of our Sun