O-LevelPhysicsKinematics5054/22 · Oct/Nov 2025 · Q910 Marks

Fig. 9.1 shows how the Sun and the rest of the Solar System orbit around the centre of the Milky Way in a circular path. [Figure 9.1]

(a)(i)The Sun travels around the circular path at a speed v. The speed of light in a vacuum is 9.5 × 10¹² km/year. The Sun is 26000 light-years from the centre of the Milky Way. Determine the distance from the Sun to the centre of the Milky Way in kilometres (km).[2]
(a)(ii)It takes the Sun 2.3 × 10⁸ years to complete one orbit around the centre of the Milky Way. Calculate the speed v.[2]
(b)(i)Astronomical observations suggest that, at the centre of the Milky Way, there is a black hole. Black holes are produced from red supergiants. Near the end of its life, a massive star becomes a red supergiant. Describe what happens inside the star as it becomes a red supergiant.[2]
(b)(ii)Describe how a red supergiant produces a black hole.[3]
(b)(iii)Describe how the heaviest elements are produced.[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] (a)(i) 9.5 × 10^12 (km) × 26 000 or 2.5 × 10^17 (km) seen
[1] (a)(i) 2.5 × 10^17 (km)
[1] (a)(ii) (v =) 2πr / T or (2π × 26 000) / (2.3 × 10^8) (x 3.0 × 10^8) or (2π × 2.5 × 10^20) / (2.3 x 10^8 x 365 × 24 × 3600)
[1] (a)(ii) 2.1 x 10^5 (m/s) or 2.2 × 10^5 (m/s)
[1] (b)(i) most of the hydrogen has been converted to helium/it runs out of hydrogen/fuel
[1] (b)(i) (outer region) expands /(radiation pushes) the surface of the star outwards
[1] (b)(i) centre of star/core contracts or centre of star/core becomes hotter
[1] (b)(i) hydrogen surrounding centre of star/core begins to fuse/burn
[1] (b)(i) radiation pressure increases
[1] (b)(ii) (red supergiant/it) explodes
[1] (b)(ii) (as a) supernova
[1] (b)(ii) producing a nebula (and leaving behind a black hole)
[1] (b)(iii) (in a supernova explosion) lighter nuclei/elements joined / forced together/small nuclei fuse

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