OxfordAQA International GCSE Physics: Solar system, orbits, red shift, Big Bang (9203) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions are written for the OxfordAQA International GCSE Physics (9203) specification, for exams May/June 2018 onwards. They cover sections 3.8.2 (solar system and orbital motion) and 3.8.3 (red shift and the expanding universe). The qualification is untiered, and section 3.8.3 is for the full Physics award only.

Read the study guide first if a topic is new, and use the revision notes afterwards. Use the course hub and the printable checklist to track progress, and the 10-minute diagnostics to find weak spots.

Use: speed of sound in air 340 m/s; 1 day = 86 400 s.

Questions

1. State two differences between a planet and a moon, and one difference between an asteroid and a comet. [3]

2. Describe what the Milky Way is, and state roughly how many stars it contains. [2]

3. Compare a geostationary orbit with a low polar orbit. Include one difference in position or period and one use of each. [4]

4. A satellite in a low polar orbit has an orbital radius of 7.05 × 10⁶ m and takes 5890 s to complete one orbit.

(a) Calculate its orbital speed. Give your answer to 3 significant figures. [3] (b) Calculate the number of complete orbits it makes in 24 hours. [2]

5. A planet moves round the Sun at constant speed on a nearly circular path. Explain why the planet is accelerating. [4]

6. Two satellites orbit the Earth. Satellite A has an orbital radius of 8.0 × 10⁶ m and an orbital period of 7120 s. Satellite B has an orbital radius of 2.0 × 10⁷ m and an orbital period of 28 100 s.

(a) Calculate the speed of satellite A. [2] (b) Calculate the speed of satellite B. [2] (c) Explain, in terms of gravity, why the two speeds are different. [3]

7. A siren on a stationary vehicle emits sound of frequency 800 Hz. A listener stands by the road. The vehicle then drives towards the listener, and the listener hears a frequency of 860 Hz.

(a) Calculate the wavelength of the sound emitted when the vehicle is stationary. [2] (b) Calculate the wavelength of the sound the listener receives while the vehicle approaches. [2] (c) Describe and explain what the listener hears after the vehicle has passed and is driving away. [2]

8. A spectral line from sodium has a wavelength of 589.0 nm in the laboratory. The same line is measured in the light from three galaxies.

Galaxy	Distance (million light-years)	Recession speed (km/s)	Observed wavelength (nm)
X	120	2500	593.9
Y	350	7300	603.3
Z	700	14 600	617.7

(a) Calculate the increase in wavelength for each galaxy. [2] (b) Describe the pattern shown by the data. [2] (c) State what this pattern suggests about the universe. [2]

9. Explain how the red shift of light from distant galaxies provides evidence for the Big Bang model. [4]

10. State what cosmic microwave background radiation (CMBR) is, where it comes from, and why it is important to the Big Bang theory. [3]

11. A moon orbits a distant planet at a radius of 1.9 × 10⁸ m. It takes 4.2 days for one orbit.

(a) Calculate the orbital speed of the moon. [3] (b) A second moon of the same planet orbits closer to the planet. State, with a reason, how its orbital speed compares with the first moon. [2] (c) Explain how the planet keeps the first moon moving in a circle. [3]

12. Scientists believe the universe is 14 thousand million years old.

(a) Write this age in years in standard form. [1] (b) Light from a galaxy has travelled for 3.5 thousand million years to reach us. State how old the universe was when the light set off. [2] (c) A student says that red shift alone proves the Big Bang. Evaluate this statement, using the evidence from section 3.8.3. [4]

Answers

1. A planet orbits the Sun but a moon orbits a planet [1]; a moon is smaller than the planet it orbits (or a planet is larger) [1]; asteroids are small rocky bodies, mostly in a belt, whereas comets are ice and dust on long stretched-out orbits [1] [3] Examiner insight: A comparison needs both bodies in each statement, so write “larger than” or “orbits the Sun, not a planet” rather than describing only one object.

2. The Milky Way is the galaxy that contains the Sun and our solar system [1]; it contains thousands of millions of stars [1] [2] Examiner insight: Say “galaxy” and give the size as thousands of millions; answers that call it a solar system or give a small figure lose credit.

3. Geostationary: above the equator at about 36 000 km, taking 24 hours for one orbit, so it stays above one point [1]; use: communications or television [1]. Low polar: passes over the poles at a much lower height with a shorter period, about an hour and a half [1]; use: mapping or weather monitoring, as the Earth turns beneath it [1] [4] Examiner insight: Put a difference and a use for each orbit in separate sentences so each point is clear; a use matched to the wrong orbit is a common slip.

4. (a) Distance = 2πr = 2π × 7.05 × 10⁶ [1] = 4.43 × 10⁷ m. Speed = distance / time = 4.43 × 10⁷ / 5890 [1] = 7520 m/s [1] [3] (b) 86 400 / 5890 = 14.7 [1], so 14 complete orbits [1] [2] Examiner insight: Show the substitution into distance / time and give the unit; rounding 14.7 up to 15 answers a different question from “complete orbits”.

5. Gravity from the Sun acts on the planet towards the centre of the orbit [1]; this force is at right angles to the direction of motion, so it changes direction but not speed [1]; velocity is speed in a given direction, so changing direction changes the velocity [1]; a change in velocity is an acceleration, so the planet accelerates towards the centre of the orbit [1] [4] Examiner insight: Separate speed from velocity in your wording; saying the planet “has constant speed so cannot accelerate” is the idea the question is testing.

6. (a) Speed = 2π × 8.0 × 10⁶ / 7120 [1] = 7060 m/s [1] [2] (b) Speed = 2π × 2.0 × 10⁷ / 28 100 [1] = 4470 m/s [1] [2] (c) Satellite B is further from the Earth, so the force of gravity on it is smaller [1]; this smaller centripetal force can only keep it in orbit at a lower speed [1]; so the larger radius goes with the lower orbital speed (A is faster) [1] [3] Examiner insight: Link radius to gravity and gravity to speed in that order; “B is slower because it is further away” without mentioning gravity leaves the reasoning incomplete.

7. (a) Wavelength = wave speed / frequency = 340 / 800 [1] = 0.425 m [1] [2] (b) Wavelength = 340 / 860 [1] = 0.395 m (shorter than 0.425 m) [1] [2] (c) The frequency heard is lower than 800 Hz, so the pitch drops [1]; the wavelength heard is longer, because the source is moving away (Doppler effect) [1] [2] Examiner insight: State both the wavelength change and the frequency change, and link each to the direction of the source; the wave equation is the quickest route in parts (a) and (b).

8. (a) X: 593.9 − 589.0 = 4.9 nm [1]; Y: 14.3 nm and Z: 28.7 nm [1] [2] (b) All three wavelengths are longer than the laboratory value (red shift) [1]; the more distant the galaxy, the larger the shift and the faster the recession speed [1] [2] (c) The galaxies are moving away from us, with the more distant ones moving faster [1]; this suggests that space itself is expanding [1] [2] Examiner insight: A pattern needs the trend in the data, with values quoted, not only “it goes up”; the conclusion should refer to the universe as a whole.

9. Light from most distant galaxies is shifted to longer wavelength (red shift) [1]; the further away the galaxy, the larger the shift and the faster it is moving away [1]; this suggests that space is expanding [1]; so in the past everything was closer together, which fits the Big Bang model, where the universe started as one tiny point [1] [4] Examiner insight: Chain the argument from observation to expansion to a small beginning; an answer that stops at “galaxies are moving away” has not reached the Big Bang.

10. CMBR is electromagnetic radiation in the microwave region that fills the universe [1]; it is left over from radiation that existed soon after the universe began [1]; currently only the Big Bang theory explains its existence, so it supports the theory [1] [3] Examiner insight: Name the type of wave and say where it comes from; “background noise from space” is too vague to answer the question.

11. (a) Time = 4.2 × 86 400 = 3.63 × 10⁵ s [1]; distance = 2π × 1.9 × 10⁸ = 1.19 × 10⁹ m [1]; speed = 1.19 × 10⁹ / 3.63 × 10⁵ = 3290 m/s [1] [3] (b) Its speed is higher [1]; the radius is smaller, so gravity is stronger and a higher speed goes with the stable orbit [1] [2] (c) The planet’s gravity acts on the moon towards the centre of the orbit [1]; this is the centripetal force, an unbalanced force towards the centre [1]; it changes the direction of the moon’s velocity but not its speed [1] [3] Examiner insight: Convert days to seconds before dividing and keep the time and distance on separate lines; in part (c) name gravity as the centripetal force instead of describing a “pull” in general terms.

12. (a) 1.4 × 10¹⁰ years [1] [1] (b) 14 − 3.5 [1] = 10.5 thousand million years old [1] [2] (c) Red shift shows that distant galaxies are moving away, so space is expanding, which supports the Big Bang [1]; but red shift is only one piece of evidence [1]; CMBR is a second, independent piece, radiation from shortly after the beginning [1]; currently only the Big Bang theory explains CMBR, so together they give strong support, but “proves” is too strong a word for a scientific model [1] [4] Examiner insight: For an evaluate question, give a judgement and support it with both pieces of evidence; saying only that the student is right or wrong leaves the reasoning unshown.

Where marks are usually lost

• Describing the speed of an orbiting body as changing, instead of the direction of its velocity.
• Using the height above the surface instead of the radius from the centre of the Earth.
• Not converting days or hours into seconds before dividing.
• Mixing up the Doppler effect: a receding source gives longer wavelength and lower frequency.
• Calling a geostationary satellite stationary. It orbits once every 24 hours.
• Using red shift as the only evidence when two pieces are asked for.
• Writing the age of the universe as 14 million years.

Next steps

• Re-read the revision notes for the points you missed.
• Revisit the study guide for full explanations.
• Tick off the printable checklist at the course hub.
• Try the all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Physics (9203), specification for exams May/June 2018 onwards, published by OxfordAQA. Sections 3.8.2 and 3.8.3.