宇宙中的運動：練習題

Which of the following correctly describes the hierarchy of structures in the universe?

An astronaut has a weight of \( 750 \text{ N} \) on Earth, where the gravitational field strength is \( 10 \text{ N/kg} \). On Planet X, the gravitational field strength is \( 3.7 \text{ N/kg} \).

What is the astronaut's mass on Planet X?

The gravitational field strength \( g \) varies on different planets. Which of the following explains why a moon orbiting a very massive planet must travel faster than a moon orbiting a less massive planet at the same orbital radius?

Our Solar System is located within a large collection of stars. What is the correct name for this collection of stars and the galaxy we belong to?

A satellite orbits the Earth at a constant speed in a circular orbit of radius \( 42,000 \text{ km} \). If the orbital period is exactly \( 24 \text{ hours} \), calculate the orbital speed in \( \text{km/s} \).

State the name of the force that provides the centripetal force required to keep a moon in a circular orbit around a planet.

An artificial satellite orbits the Earth at an orbital radius of \( 7500 \text{ km} \) and completes one orbit in \( 1.5 \text{ hours} \). Calculate its orbital speed in \( \text{km/h} \).

A planet orbits a star at a distance of \( 2.0 \times 10^{8} \text{ km} \) with a constant orbital speed of \( 40 \text{ km/s} \). Calculate the time taken for one complete orbit, giving your answer in days. (Assume \( 1 \text{ day} = 86400 \text{ s} \))

A satellite orbits the Earth at a constant altitude. The radius of the Earth is approximately \( 6400 \text{ km} \) and the satellite is orbiting \( 400 \text{ km} \) above the Earth's surface. The satellite completes one full orbit every \( 95 \text{ minutes} \).

(a) Calculate the orbital radius of the satellite in metres.
(b) Calculate the orbital speed of the satellite in \( \text{m/s} \). Give your answer to 3 significant figures.

The diagram represents the orbits of a planet and a comet around the Sun. The planet follows a nearly circular path, while the comet follows a highly elliptical path.

(a) Describe three differences between the orbits of a comet and a planet.
(b) A comet travels much faster when it is closer to the Sun than when it is far away. Explain this change in speed in terms of energy stores.
(c) The Moon orbits the Earth. Explain the role of gravitational force in this motion.