試題詳解

32. A rocket moving in space, far from all other objects, has a speed of vi relative to the Earth. Its engines are turned on, and fuel is ejected in a direction opposite to the rocket’s motion at a speed of vrel relative to the rocket. What is the speed of the rocket, vf relative to the earth once the rocket’s mass is reduced to half its mass before ignition?
(A) v_i+ v_rel ln2
(B) v_i+ v_rel ln(1/2)
(C) v_i+ 2_vrel
(D) (v_i+ v_rel) / 2
(E) v_i+ v_rel / 2