Suppose a spacecraft is moving in a region of space where the gravitational force acting upon it is negligible. Suggest how can it change its velocity. [Pg. No. 110]

In space, where external forces are negligible, a spacecraft changes its velocity by using rocket engines. The engines throw gases backward at high speed, and in reaction, the spacecraft moves forward or changes direction. This happens due to Newton's third law of motion: Every action has an equal and opposite reaction.