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GCSE · Physics

P8a The Solar System, Orbital Motion and Satellites

AQA 8463 · Calculator allowed · about 85 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Key words and equations: the Solar System, orbital motion and satellites (P8a)

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The Solar System consists of the Sun (a star) and the objects that orbit it: eight planets, their natural satellites (moons), dwarf planets, asteroids and comets. A star forms from a nebula, a cloud of dust and gas, which is pulled together by gravity to form a protostar; once the core becomes hot and dense enough, nuclear fusion begins and a new star is born. For most of its life, a star sits on the main sequence, a long, stable period in which nuclear fusion of hydrogen into helium in its core balances the inward pull of gravity. A star with a similar mass to the Sun eventually becomes a red giant, then loses its outer layers to leave a white dwarf, which cools over a very long time into a black dwarf. A much more massive star becomes a red super giant, then explodes as a supernova, leaving behind either a neutron star or, if the remaining core is massive enough, a black hole; elements heavier than iron are only formed during a supernova explosion. An object moving in a circular orbit has a constantly changing direction of velocity, so it is always accelerating towards the centre of the orbit; this centripetal acceleration is caused by a centripetal force, which for an orbiting planet, moon or satellite is provided by gravitational attraction. For a stable orbit, an orbit with a larger radius requires a slower orbital speed, because gravitational force is weaker at greater distances. Equation used in this worksheet: orbital speed = (2 x pi x orbital radius) / time period (v = 2 x pi x r / T). A satellite is an object that orbits a larger object; a geostationary satellite orbits above the equator with a time period of 24 hours, staying above the same point on the Earth's surface, while a low polar orbit satellite orbits much closer to the Earth with a much shorter time period, passing over a different strip of the Earth's surface on each orbit.

The Solar System contains many different types of object, all orbiting the Sun (directly or indirectly).

(a)State what type of object the Sun is.(1)

(b)Name the objects that orbit the Sun directly, such as Earth and Jupiter.(1)

(c)Name the objects that orbit planets, such as the Moon orbiting the Earth.(1)

(d)Name two other types of smaller object found in the Solar System, in addition to planets and their moons.(1)

(Total for Question 1 is 4 marks)

The Solar System, including the Sun and the planets, formed billions of years ago from a cloud of dust and gas.

(a)Name this initial cloud of dust and gas.(1)

(b)Name the force that causes the cloud to collapse and be pulled together.(1)

(c)Explain what happens to the material at the centre of the collapsing cloud, and what this eventually becomes.(2)

(Total for Question 2 is 4 marks)

A star with a mass similar to the Sun passes through several stages during its life cycle.

(a)Put these four stages in the correct order, starting with the earliest: main sequence star, protostar, red giant, white dwarf.(3)

(b)State what a white dwarf eventually becomes, once it has cooled down completely and stopped glowing.(1)

(c)State the source of energy that keeps a star stable and glowing during the main sequence stage.(1)

(Total for Question 3 is 5 marks)

A star with a much greater mass than the Sun follows a different path after the main sequence.

(a)State the stage that a very massive star enters after leaving the main sequence, before it explodes.(1)

(b)Name the explosive event that ends the life of a red super giant.(1)

(c)State the two objects that a supernova can leave behind, and identify the factor that determines which one forms.(3)

(Total for Question 4 is 5 marks)

Elements are created within the life cycle of a star.

(a)State the process, and the location within a star, by which elements up to iron are formed.(2)

(b)State when elements heavier than iron are formed.(1)

(Total for Question 5 is 3 marks)

A planet orbits the Sun in a stable, roughly circular orbit.

Figure (to be drawn): A planet moving in a circular orbit around the Sun. Arrows are drawn at one point on the orbit: a velocity arrow tangent to the circle, and a force arrow pointing from the planet directly towards the Sun at the centre.

(a)Name the force that keeps the planet in its orbit.(1)

(b)State the direction of this force, relative to the centre of the orbit.(1)

(c)The planet moves at a constant speed around its orbit. Explain why the planet is still accelerating, even though its speed does not change.(2)

(Total for Question 6 is 4 marks)

For a stable circular orbit, the gravitational force provides exactly the centripetal force needed to keep an object moving in a circle at that radius.

(a)State what happens to the strength of the gravitational force between two objects as the distance between them increases.(1)

(b)Use this idea to explain why an object in a stable orbit at a large orbital radius has a lower orbital speed than an object in a stable orbit at a small orbital radius.(3)

(Total for Question 7 is 4 marks)

Satellites can be natural or artificial.

(a)Give one example of a natural satellite, other than the Moon.(1)

(b)State two uses of artificial satellites.(2)

(Total for Question 8 is 3 marks)

A geostationary satellite is used for continuous communication with a fixed region on the Earth's surface.

(a)State the orbital period of a satellite in a geostationary orbit.(1)

(b)State the plane in which a geostationary satellite orbits, relative to the Earth.(1)

(c)Explain why a geostationary orbit is useful for a satellite television broadcasting company.(1)

(Total for Question 9 is 3 marks)

A low polar orbit satellite is used to monitor the Earth's whole surface for weather forecasting.

(a)State one feature of the orbit that makes it a low polar orbit.(1)

(b)State how the orbital period of a low polar orbit satellite compares with that of a geostationary satellite.(1)

(c)Explain why a low polar orbit is useful for monitoring the whole of the Earth's surface over time.(1)

(Total for Question 10 is 3 marks)

Orbital speed, orbital radius and time period are linked by a single equation.

(a)Write down the equation linking orbital speed, orbital radius and time period.(1)

(b)State the SI unit of orbital speed.(1)

(Total for Question 11 is 2 marks)

A small satellite orbits the Earth at an orbital radius of 7.0 x 10⁶ m, with a time period of 5800 s. Use the Physics Equations Sheet. Use the equation: orbital speed = (2 x π x orbital radius) / time period.

(a)Calculate the orbital speed of the satellite.(3)

(Total for Question 12 is 3 marks)

Higher Tier only. A satellite completes one orbit of the Earth in a time period of 7200 s, at an orbital speed of 6800 m/s. Use the Physics Equations Sheet. Use the equation: orbital speed = (2 x π x orbital radius) / time period.

(a)Rearrange the equation to make orbital radius the subject.(1)

(b)Calculate the orbital radius of the satellite.(3)

(Total for Question 13 is 4 marks)

Satellite P orbits at a smaller radius than satellite Q, and both are in stable circular orbits around the Earth.

(a)State which satellite, P or Q, has the greater orbital speed.(1)

(b)State which satellite, P or Q, has the longer time period for one orbit.(1)

(Total for Question 14 is 2 marks)

The table shows the approximate orbital radius and orbital period for four types of satellite orbit.
Orbit type: Low Earth orbit, Medium Earth orbit, Geostationary orbit, Distant orbit
Orbital radius (x10⁶ m): 6.8, 20, 42, 80
Orbital period (hours): 1.5, 12, 24, 63

(a)Describe the relationship shown by the data between orbital radius and orbital period.(2)

(b)Use the data to state which of the four orbit types would give a satellite the fastest orbital speed.(1)

(Total for Question 15 is 3 marks)

A company is designing a new satellite to provide continuous, real-time internet coverage to a single fixed region of the United Kingdom. They are choosing between placing the satellite in a geostationary orbit or a low polar orbit. Evaluate which type of orbit would be more suitable for this purpose. In your answer, you should consider: the orbital period and altitude of each orbit type; how each orbit type would affect the satellite's position relative to the region being served; any other relevant advantages or disadvantages of each orbit.

(Total for Question 16 is 6 marks)

The Moon orbits the Earth, and the Earth orbits the Sun.

(a)State what provides the centripetal force that keeps the Moon in orbit around the Earth.(1)

(b)The Earth takes 1 year to orbit the Sun, and the Moon takes about 1 month to orbit the Earth. Using ideas about orbital radius, suggest why the Moon completes many more orbits of the Earth in a year than the Earth completes orbits of the Sun.(2)

(Total for Question 17 is 3 marks)

Pluto is classified as a dwarf planet, not a full planet, even though it orbits the Sun. Comets and asteroids are also smaller objects found within the Solar System.

(a)State one similarity between a dwarf planet and a planet.(1)

(b)State one difference between a comet and an asteroid.(2)

(Total for Question 18 is 3 marks)

A student incorrectly says that a star like the Sun produces energy by burning hydrogen gas, in the same way a fire burns fuel.

(a)State the correct process by which the Sun produces energy.(1)

(b)Explain why this process is different from ordinary burning (combustion).(2)

(Total for Question 19 is 3 marks)

The life cycle of a star depends on its mass.

(a)State one similarity between the life cycle of a star similar in mass to the Sun and a star with a much greater mass than the Sun.(1)

(b)State one key difference between the two life cycles, after the main sequence stage.(2)

(Total for Question 20 is 3 marks)

Mark scheme · P8a The Solar System, Orbital Motion and Satellites

Question 1

(a) B1 a star
(a) Answer: A star.
(b) B1 planets
(b) Answer: Planets.
(c) B1 (natural) satellites/moons
(c) Answer: Natural satellites (moons).
(d) B1 any two of: dwarf planets; asteroids; comets
(d) Answer: Any two of: dwarf planets, asteroids, comets.

Question 2

(a) B1 nebula
(a) Answer: Nebula.
(b) B1 gravity (gravitational attraction)
(b) Answer: Gravity.
(c) B1 the material at the centre becomes increasingly hot, dense and compressed as more material is pulled in by gravity
(c) B1 eventually this becomes hot and dense enough for nuclear fusion to begin, forming a new star, oe
(c) Answer: The material at the centre becomes hotter and denser until nuclear fusion begins, forming a new star.

Question 3

(a) B1 protostar placed before main sequence star
(a) B1 main sequence star placed before red giant
(a) B1 red giant placed before white dwarf
(a) Answer: protostar, main sequence star, red giant, white dwarf
(b) B1 black dwarf
(b) Answer: Black dwarf.
(c) B1 nuclear fusion of hydrogen (into helium) in the star's core
(c) Answer: Nuclear fusion of hydrogen into helium.

Question 4

(a) B1 red super giant (red supergiant)
(a) Answer: Red super giant.
(b) B1 supernova
(b) Answer: Supernova.
(c) B1 neutron star
(c) B1 black hole
(c) B1 depends on the mass of the remaining core/original star - only a sufficiently massive star leaves behind a black hole, oe
(c) Answer: A neutron star or a black hole; a black hole only forms from a sufficiently massive remaining core.

Question 5

(a) B1 nuclear fusion
(a) B1 in the core of the star
(a) Answer: Nuclear fusion, in the core of the star.
(b) B1 during a supernova explosion
(b) Answer: During a supernova explosion.

Question 6

(a) B1 gravitational force (of attraction between the Sun and the planet)
(a) Answer: Gravitational force.
(b) B1 towards the centre of the orbit (towards the Sun)
(b) Answer: Towards the centre of the orbit.
(c) B1 velocity depends on both speed and direction, and although the speed is constant, the direction of the planet's motion is continuously changing
(c) B1 a change in velocity means the planet is accelerating, with the acceleration directed towards the centre of the orbit, oe
(c) Answer: Its direction keeps changing, so velocity changes, so it is accelerating towards the centre of the orbit.

Question 7

(a) B1 the gravitational force decreases (gets weaker)
(a) Answer: It decreases.
(b) B1 at a larger orbital radius, the gravitational force is weaker
(b) B1 a weaker force provides a smaller centripetal force
(b) B1 a smaller centripetal force is needed to keep an object moving in a circle at a lower speed, so the orbital speed needed for a stable orbit is lower at a larger radius, oe
(b) Answer: Weaker gravity at a larger radius provides less centripetal force, which is only enough to hold an object in a stable orbit if it moves more slowly.

Question 8

(a) B1 any moon of another planet, e.g. a moon of Jupiter or Saturn
(a) Answer: E.g. a moon of Jupiter.
(b) B1 first correct use, e.g. communications (television/phone signals); weather monitoring/forecasting; satellite navigation (GPS-type systems); Earth observation/environmental monitoring; scientific research/astronomy
(b) B1 second correct use, different from the first (from the same list)
(b) Answer: Any two of: communications, weather monitoring, satellite navigation, Earth observation, scientific research.

Question 9

(a) B1 24 hours (1 day)
(a) Answer: 24 hours.
(b) B1 above the equator (in the plane of the equator)
(b) Answer: Above the equator.
(c) B1 the satellite stays above the same point on the Earth's surface at all times, since its orbital period matches the Earth's rotation, so a satellite dish on the ground can stay pointed in a fixed direction, oe
(c) Answer: It stays above the same point, so ground dishes never need to move.

Question 10

(a) B1 it orbits at a low altitude, close to the Earth's surface, passing near/over the North and South poles on each orbit, oe
(a) Answer: It orbits close to the Earth, passing near the poles.
(b) B1 it is much shorter (much less than 24 hours)
(b) Answer: It is much shorter.
(c) B1 the satellite passes over a different strip of the Earth's surface on each orbit, as the Earth rotates beneath it, so given enough time it can image/monitor the whole surface, oe
(c) Answer: It passes over a different strip of the Earth each orbit as the Earth turns, eventually covering the whole surface.

Question 11

(a) B1 orbital speed = (2 x π x orbital radius) / time period
(a) Answer: orbital speed = (2 x π x orbital radius) / time period
(b) B1 metres per second, m/s
(b) Answer: Metres per second (m/s).

Question 12

(a) M1 substitution: v = (2 x π x 7.0 x 10⁶) / 5800, oe
(a) M1 correct evaluation of the numerator: 2 x π x 7.0 x 10⁶ = 4.398 x 10⁷
(a) A1 v = 7580 m/s (3 s.f.), cao (accept awrt 7580 m/s)
(a) Answer: v = 7580 m/s

Question 13

(a) B1 orbital radius = (orbital speed x time period) / (2 x π)
(a) Answer: r = (v x T) / (2 x π)
(b) M1 substitution: r = (6800 x 7200) / (2 x π), oe
(b) M1 correct evaluation of the numerator: 6800 x 7200 = 4.896 x 10⁷
(b) A1 r = 7.79 x 10⁶ m (3 s.f.), cao (accept awrt 7.79 x 10⁶ m)
(b) Answer: r = 7.79 x 10⁶ m

Question 14

(a) B1 satellite P
(a) Answer: Satellite P.
(b) B1 satellite Q
(b) Answer: Satellite Q.

Question 15

(a) B1 as orbital radius increases, orbital period increases
(a) B1 the increase is not directly proportional - the period increases more steeply than the radius (e.g. radius increases by a factor of about 12 from Low Earth orbit to Distant orbit, but the period increases by a factor of 42), oe
(a) Answer: Orbital period increases as orbital radius increases, but not in direct proportion; period increases more steeply than radius.
(b) B1 Low Earth orbit - it has both the smallest orbital radius and the shortest orbital period, oe
(b) Answer: Low Earth orbit.

Question 16

Level 0 (0): No relevant content.
Level 1 (1-2): Isolated statement(s) are made about one orbit type, with little or no evaluation.
Level 2 (3-4): Relevant points are made about both orbit types, with some comparison, but the conclusion may not be clearly justified.
Level 3 (5-6): A detailed, well-reasoned evaluation of both orbit types is given, leading to a clearly justified conclusion, with correct scientific vocabulary throughout.
Indicative content:
- A geostationary orbit has a time period of 24 hours and stays above the same point on the Earth's equator/surface at all times.
- This means a satellite dish on the ground could stay pointed in one fixed direction, useful for continuous coverage of a single fixed region.
- A geostationary orbit is at a very high altitude, so the signal travels a long distance, which can introduce a noticeable delay in real-time communication.
- A low polar orbit satellite orbits at a much lower altitude, closer to the Earth, giving a shorter signal delay.
- However, a low polar orbit satellite moves quickly relative to the ground and only passes over the UK for a short time on each orbit, so continuous coverage of a single fixed region would need a large constellation of many satellites working together.
- A single geostationary satellite can provide constant coverage of a fixed region, whereas a single low orbit satellite cannot.
- A valid conclusion: for continuous single-region coverage with minimal ground equipment, a geostationary orbit is more suitable overall, though a low-orbit constellation could offer a lower signal delay if enough satellites are used, oe (accept a different, well-justified conclusion).

Question 17

(a) B1 the gravitational force between the Earth and the Moon
(a) Answer: Gravitational force between the Earth and the Moon.
(b) B1 the Moon's orbital radius around the Earth is much smaller than the Earth's orbital radius around the Sun
(b) B1 a smaller orbital radius corresponds to a much shorter time period, so the Moon completes far more orbits in the same amount of time, oe
(b) Answer: The Moon's orbit has a much smaller radius, giving a much shorter time period, so it completes far more orbits per year.

Question 18

(a) B1 e.g. both orbit the Sun / both are roughly spherical due to their own gravity
(a) Answer: E.g. both orbit the Sun.
(b) B1 a comet is made mostly of ice, dust and rock, and develops a visible tail as it nears the Sun
(b) B1 an asteroid is made mostly of rock and/or metal, and does not typically develop a tail, oe (accept the converse ordering)
(b) Answer: A comet is icy and develops a tail near the Sun; an asteroid is rocky/metallic and does not.

Question 19

(a) B1 nuclear fusion (of hydrogen nuclei to form helium)
(a) Answer: Nuclear fusion.
(b) B1 nuclear fusion involves the nuclei of atoms joining together, releasing energy from within the nucleus, not a chemical reaction with oxygen
(b) B1 ordinary burning/combustion is a chemical reaction between a fuel and oxygen, releasing much less energy per kilogram of fuel than nuclear fusion, oe
(b) Answer: Fusion joins atomic nuclei together, releasing far more energy than the chemical reaction of burning with oxygen.

Question 20

(a) B1 e.g. both begin as a nebula and pass through a main sequence stage powered by nuclear fusion, oe
(a) Answer: E.g. both pass through a main sequence stage.
(b) B1 a Sun-sized star ends as a white dwarf (then a black dwarf), while a massive star explodes as a supernova
(b) B1 a massive star can leave behind a neutron star or black hole, which a Sun-sized star's life cycle never produces, oe
(b) Answer: A Sun-sized star ends as a white/black dwarf; a massive star explodes as a supernova, leaving a neutron star or black hole.

The Solar System, Orbital Motion and Satellites - Worksheets, Questions and Revision