試題詳解

5. A space craft is launched from the surface of the Earth with a heliocentric speed of 42 km/s (the speed relative to the Sun). What is its speed when it reaches a distance of 5 AU from the Sun? Note: you have to include the gravitational potential of the Earth as well as the Sun in the calculation.
(A) 12 km/s；
(B) 15km/s；
(C)18 km/s；
(D) 21 km/s；
(E) 24km/s.