Question

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which statements about weightlessness in orbit are correct?

□ earth’s gravitational field is negligible in orbit.
□ the apparent weight of an astronaut in orbit is zero, even though the actual weight is almost the same as on earth.
□ the orbital velocity overcomes the acceleration due to gravity, with the result that free - fall acceleration is zero.
□ free - fall acceleration is slightly less on a 400 - km orbit than at earth’s surface, but this is not the reason that astronauts feel weightless.

Explanation:

• Earth’s gravitational field is not negligible in orbit; it provides the centripetal force for orbiting.
• Apparent weight is zero in orbit because both the astronaut and the spacecraft are in free fall (no normal force), while actual weight (due to gravity) is nearly Earth-surface value.
• Orbital velocity does not eliminate free-fall acceleration; gravity causes continuous free fall, leading to weightlessness.
• Free-fall acceleration decreases slightly with altitude (e.g., 400-km orbit), but weightlessness arises from free fall, not this small decrease.

Answer:

The apparent weight of an astronaut in orbit is zero, even though the actual weight is almost the same as on Earth.
Free-fall acceleration is slightly less on a 400-km orbit than at Earth’s surface, but this is not the reason that astronauts feel weightless.