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IGCSE · 6 · multiple choice

Space physics · Question 3

Space physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.

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Answer
Complete
A planet in a circular orbit around its starstarplanet1.1 × 10¹¹ mdirection of travelone complete orbit takes 1.9 × 10⁷ s
Fig. 3.1A planet moving on a nearly circular orbit around its star. The star is a disc at the centre of a dashed circle and the planet is a smaller disc on that circle, level with the star and to its right. The distance from the centre of the star out to the planet is marked 1.1 × 10¹¹ m, an arrow at the planet points along the orbit to show the direction in which it travels, and a note beneath states that one complete orbit takes 1.9 × 10⁷ s.
multiple choice1 mark

A planet orbits its star in a nearly circular path of radius 1.1 × 10¹¹ m, taking 1.9 × 10⁷ s to complete one orbit. What is its average orbital speed?

  1. A

    5.8 × 10³ m/s

  2. B

    1.8 × 10⁴ m/s

  3. C

    3.6 × 10⁴ m/s

  4. D

    5.8 × 10⁴ m/s

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Answer overviewCorrect answer: C — 3.6 × 10⁴ m/s
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is C: 3.6 × 10⁴ m/s

  2. 2

    A divides the radius by the time and forgets the circumference entirely. B uses πr rather than 2πr, which is the commonest slip once the candidate has remembered that a circumference is involved.

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