Earth, Moon and Solar System — GCSE Physics practice questions

Question 1

Astronomers have found a small icy world far beyond Neptune and have classed it as a dwarf planet.

Which statement about the Solar System is correct?

Accepted Answer

A: It has one star, eight planets and many smaller bodies such as dwarf planets, asteroids and comets.. The Solar System has one star, the Sun, and eight planets. It also contains minor planets (dwarf planets and the asteroids of the asteroid belt between Mars and Jupiter), moons, and smaller bodies such as comets. A dwarf planet is not counted as a planet.

Question 2

A space probe near Jupiter is 6.3 × 10^11 m from the Earth. Engineers send a radio command to the probe, and the probe replies at once. Radio waves travel at 3.0 × 10^8 m / s.

How long after the command is sent does the reply reach the Earth?

Accepted Answer

C: 70 min. The radio waves travel to the probe and back, a distance of 2 × 6.3 × 10^11 = 1.26 × 10^12 m. t = d / c = 1.26 × 10^12 / 3.0 × 10^8 = 4200 s, which is 4200 / 60 = 70 min.

Question 3

A space telescope orbits the Earth in a circular orbit 540 km above the Earth's surface. It takes 94 minutes to complete one orbit. The radius of the Earth is 6400 km.

What is the orbital speed of the telescope in km / h?

Accepted Answer

D: 2.8 × 10^4 km / h. The orbit radius is measured from the Earth's centre: r = 6400 + 540 = 6940 km. The period is 94 / 60 = 1.57 h. v = 2πr / T = 2π × 6940 / 1.57 = 2.8 × 10^4 km / h.