O Level / IGCSE Physics chapter 6: Space physics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
56 exam-style questions on Space physics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. The Milky Way is about 100 000 light-years in diameter. How long does light take to travel from one side of the Milky Way to the other?
A
about 100 000 seconds
B
about 100 000 days
C
about 100 000 years
D
about 100 000 light-years
Show answer
Answer: C. One light-year is the distance light travels in one year, so 100 000 light-years takes light about 100 000 years. "100 000 light-years" is a distance, not a time.
2. Which object contains most of the mass of the Solar System?
A
Jupiter
B
the Sun
C
the asteroid belt
D
the Earth
Show answer
Answer: B. The Sun contains almost all (over 99%) of the mass of the Solar System; Jupiter is the most massive planet but far less massive than the Sun.
3. What powers a stable star like the Sun?
A
burning of hydrogen gas in oxygen
B
nuclear fission of uranium
C
nuclear fusion of hydrogen into helium
D
gravitational collapse alone
Show answer
Answer: C. In the core, hydrogen nuclei fuse into helium, releasing energy. The outward pressure from this balances the inward pull of gravity, keeping the star stable.
4. Planet P orbits the Sun further out than planet Q. Which is correct for planet P?
A
a longer orbital period and a lower orbital speed
B
a longer orbital period and a higher orbital speed
C
a shorter orbital period and a lower orbital speed
D
the same orbital speed as Q, as both orbit the Sun
Show answer
Answer: A. The Sun's gravitational field is weaker further out, so planets there move more slowly. They also have a longer path to travel, so their orbital period is longer.
5. The Moon orbits the Earth at an average radius of 3.8 × 108 m with an orbital period of 27 days. What is its average orbital speed?
A
1.6 × 102 m/s
B
1.0 × 103 m/s
C
3.7 × 106 m/s
D
8.8 × 107 m/s
Show answer
Answer: B. T = 27 × 24 × 3600 = 2.33 × 106 s. v = 2πr ÷ T = (2π × 3.8 × 108) ÷ 2.33 × 106 ≈ 1.0 × 103 m/s. Leaving T in days gives 8.8 × 107 m/s; leaving out the 2π gives 1.6 × 102 m/s.
6. A communications satellite orbits the Earth at an average radius of 4.2 × 107 m. Its orbital period is 24 hours. What is its average orbital speed?
A
4.9 × 102 m/s
B
1.5 × 103 m/s
C
3.1 × 103 m/s
D
6.1 × 103 m/s
Show answer
Answer: C. T = 24 × 3600 = 86 400 s. v = 2πr/T = 2π × 4.2 × 107 ÷ 86 400 ≈ 3.1 × 103 m/s. Leaving out 2π gives 4.9 × 102 m/s.
7. Light takes about 500 s to travel from the Sun to the Earth. Mars is about 1.5 times as far from the Sun as the Earth is. About how long does light take to travel from the Sun to Mars?
A
330 s
B
750 s
C
1000 s
D
1100 s
Show answer
Answer: B. Light travels at a constant speed, so the time is proportional to distance: 1.5 × 500 s = 750 s. 330 s comes from dividing by 1.5 instead of multiplying, and 1100 s from squaring the 1.5.
8. Which is the correct order of the planets from the Sun, starting with the nearest?
Answer: A. Mercury, Venus, Earth, Mars (the four rocky planets), then Jupiter, Saturn, Uranus, Neptune (the gas and ice giants).
9. The Milky Way is about 100 000 light-years across. One light-year is about 9.5 × 1015 m. About how wide is the Milky Way in metres?
A
9.5 × 1010 m
B
3.0 × 1013 m
C
9.5 × 1015 m
D
9.5 × 1020 m
Show answer
Answer: D. 100 000 = 105, so the width = 105 × 9.5 × 1015 = 9.5 × 1020 m. Dividing instead of multiplying gives 9.5 × 1010 m; 3.0 × 1013 m multiplies the speed of light by 100 000 without turning years into seconds.
10. Planet X has the same radius as the Earth but twice the mass. How does the gravitational field strength at the surface of X compare with that at the Earth’s surface?
A
It is half as strong
B
It is the same
C
It is zero
D
It is stronger
Show answer
Answer: D. For planets of the same size, the surface field strength depends on the mass of the planet, so the more massive planet X has a stronger surface field.
56, each with the answer and a short explanation, across 2 topics: Earth and the Solar System, Stars and the Universe. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Physics chapter 6 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
