IGCSE · 6 · structured
Space physics · Question 8
Space physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 7
- Topics
- 1
- Answer
- Complete
The table gives the orbital radius and the orbital period of four planets in the Solar System.
| planet | orbital radius / 10¹¹ m | orbital period / 10⁷ s |
|---|---|---|
| Earth | 1.50 | 3.16 |
| Mars | 2.28 | 5.94 |
| Jupiter | 7.78 | 37.4 |
| Saturn | 14.3 | 92.9 |
- (a)
Calculate Calculate the average orbital speed of Jupiter.
3 marks - (b)
Determine Without further calculation, determine whether Saturn's orbital speed is greater or smaller than Jupiter's, and justify your answer using the table.
2 marks - (c)
Explain Explain, in terms of gravitational field strength, why planets further from the Sun move more slowly.
2 marks
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(a)
Calculate Calculate the average orbital speed of Jupiter.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
v = 2πr / T
- 2
v = 2π × 7.78 × 10¹¹ / 37.4 × 10⁷
- 3
v = 1.31 × 10⁴ m/s
(b)
Determine Without further calculation, determine whether Saturn's orbital speed is greater or smaller than Jupiter's, and justify your answer using the table.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
Saturn's radius is about 1.8 times Jupiter's, but its period is about 2.5 times Jupiter's
- 2
the period grows by the larger factor, so 2πr/T is smaller — Saturn moves more slowly
(c)
Explain Explain, in terms of gravitational field strength, why planets further from the Sun move more slowly.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
the Sun's gravitational field strength decreases with distance from the Sun
- 2
so a more distant planet is held by a weaker force and a smaller speed is enough to maintain its orbit
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