The picture below shows the Apollo spacecraft that took astronauts to the moon. The spacecraft weighed about 5 million pounds, with motors that produced 7 million pounds of thrust.
Which statement explains how the spacecraft left the surface of the earth?
A. The spacecraft applied a downward force of thrust that was less than the downward force of gravity.
B. The spacecraft applied an upward force of thrust that was greater than the downward force of gravity.
C. The spacecraft applied a downward force of thrust that was equal to the downward force of gravity.
D. The spacecraft applied an upward force of thrust that was equal to the downward force of gravity.
B. The spacecraft applied an upward force of thrust that was greater than the downward force of gravity.
B. The spacecraft applied an upward force of thrust that was greater than the downward force of gravity.
To determine how the spacecraft left the surface of the earth, we need to consider Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.
In this case, the action is the thrust produced by the spacecraft's motors, and the reaction is the force of gravity pulling the spacecraft downward.
If the spacecraft were to apply a downward force of thrust that was less than the downward force of gravity (option A), the spacecraft would not be able to overcome gravity and would remain on the surface of the earth.
If the spacecraft were to apply a downward force of thrust that was equal to the downward force of gravity (option C), the forces would cancel each other out, resulting in no net force to lift the spacecraft off the surface.
If the spacecraft were to apply an upward force of thrust that was equal to the downward force of gravity (option D), the forces would again cancel each other out, resulting in no net force to lift the spacecraft off the surface.
Therefore, the correct answer is B. The spacecraft applied an upward force of thrust that was greater than the downward force of gravity. This extra upward force allowed the spacecraft to overcome the force of gravity and leave the surface of the earth, ultimately reaching the moon.