An unmanned spacecraft is in a circular orbit around the moon, observing the lunar surface from an altitude of 50.0 km (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 20.0 m/s. If nothing is done to correct its orbit, with what speed (in km/h) will the spacecraft crash into the lunar surface?

Appendix F:

Fundamental Physical Constants*

Other Useful Constants*

Astronomical Data^€ 

Prefixes for Powers of 10

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Name Symbol Value 2.99792458 x 10® m/s 1.602176487(40) × 10-1º c 6.67428(67) × 10-1! N •m²/kg² 6.62606896(33) × 10-34 J .s 1.3806504(24) × 10–23 J/K 6.02214179(30) × 1023 molecules/mol 8.314472(15) J/mol · K 9.10938215(45) × 10-31 kg 1.672621637(83) × 10-27 kg 1.674927211(84) × 10-27 kg 4m x 10-7 Wb/A•m 8.854187817... × 10-12 C²/N• m? 8.987551787... × 10º N • m²/C² Speed of light in vacuum Magnitude of charge of electron Gravitational constant G Planck's constant Boltzmann constant k NA Avogadro's number Gas constant Mass of electron me Mass of proton Mass of neutron Permeability of free space Permittivity of free space 1/Học2 1/4πεο Mechanical equivalent of heat Standard atmospheric pressure Absolute zero Electron volt Atomic mass unit Electron rest energy Volume of ideal gas (0°C and 1 atm) Acceleration due to gravity (standard) 4.186 J/cal (15° calorie) 1.01325 x 10° Pa 1 atm OK -273.15°C 1.602176487(40) × 10-19 J 1.660538782(83) x 10-27 kg 0.510998910(13) MeV 22.413996(39) liter/mol 9.80665 m/s? 1 eV mc²