An unmanned spacecraft is in a circular orbit around the moon, observing the lunar surface from an altitude of 40.0km (see Appendix F). To the dismay of scientists on earth, an electrical fault causes an on-board thruster to fire, decreasing the speed of the spacecraft by 30.0m/s. If nothing is done to correct its orbit, with what speed (in km/h) will the spacecraft crash into the lunar surface? Take the gravitational constant to be 6.673*10^-11 N*m^2/kg^2, the mass of the Moon to be 7.75*10^22, and the radius of the Moon to be 1.74*10^6. Ok, um, how do I approach this problem? I can't reason it out. Please don't do the problem for me. I really want to learn how to do this, but I just can't figure it out. Thanks in advance.