The first artificial satellite to orbit the Earth was Sputnik I, launched in the year October 4, 1957. The mass of Sputnik I was 83.5 kg, and its distances from the center of the Earth at apogee and perigee were around 7380 km and 6580 km, correspondingly. Determine the difference in gravitational potential energy for Sputnik I as it moved from apogee to perigee. (Employ a positive sign for an increase, negative sign for a decrease in U.)