A space probe leaves the solar system to explore interstellar space. Once it is far from any stars, when must it fire its rocket engines?
A) all the time, in order to keep moving
B) only when it wants to speed up
C) only when it wants to slow down
D) only when it wants to turn
E) when it wants to speed up, slow down, or turn

Question

Quizplus · Accepted Answer

In space, a probe must fire its engines to change its state of motion, including speeding up, slowing down, or changing direction. Newton's first law of motion states that an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Thus, the engines are needed for any change in velocity or direction.

A Space Probe Leaves the Solar System to Explore Interstellar