Lesson 12.3.1

12.3.1 Orbits under gravity Quiz: Pearson Edexcel Physics, Unit 12

20 questions

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Lesson 12.3.1, Orbits under gravity: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 12: Gravitational Fields, written with Revision Ninja.

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The 20 questions

  1. What provides the centripetal force for a satellite in a circular orbit?

    • Electrical attraction between the satellite and the Earth.
    • Gravitational attraction towards the centre of the planet.
    • The thrust from the satellite's engines.
    • Air resistance at the orbital height.

  2. Which expression gives the orbital speed v of a satellite at radius r about a mass M?

    • v = sqrt(G M r)
    • v = G M r^2
    • v = sqrt(G M / r)
    • v = G M / r

  3. What is the period of a geostationary satellite?

    • 12 hours
    • 24 hours
    • 365 days
    • 1 hour

  4. What is the relationship between orbital period T and radius r for a satellite about a planet?

    • T is proportional to r
    • T is proportional to 1/r
    • T^2 is proportional to r
    • T^2 is proportional to r^3

  5. Why do astronauts in orbit appear weightless?

    • The Earth's gravity cancels with the Moon's gravity in orbit.
    • They and the spacecraft are in free fall, with gravity providing the centripetal acceleration.
    • There is no gravity at the height of the orbit.
    • Air pressure in the spacecraft cancels their weight.

  6. A satellite orbits at radius 7.0 x 10^6 m about a planet with GM = 4.0 x 10^14 m^3 s^-2. What is its orbital speed?

    • 2.6 x 10^2 m s^-1
    • 1.1 x 10^4 m s^-1
    • 5.4 x 10^3 m s^-1
    • 7.6 x 10^3 m s^-1

  7. Using the satellite in the previous calculation (radius 7.0 x 10^6 m, speed about 7.6 x 10^3 m s^-1), what is its orbital period?

    • about 2.9 x 10^3 s
    • about 1.6 x 10^3 s
    • about 5.8 x 10^3 s
    • about 9.3 x 10^4 s

  8. A geostationary satellite has period 86400 s. Using GM = 4.0 x 10^14 m^3 s^-2, what is its orbital radius?

    • 1.7 x 10^5 m
    • 4.2 x 10^7 m
    • 3.6 x 10^8 m
    • 6.4 x 10^6 m

  9. If the orbital radius of a satellite is doubled, by what factor does its period change?

    • 4
    • about 2.8
    • 2
    • 8

  10. If the orbital radius of a satellite is doubled, by what factor does its orbital speed change?

    • 0.5
    • 1.41
    • about 0.71
    • 2.0

  11. The Moon orbits Earth at radius 3.8 x 10^8 m with period 2.4 x 10^6 s (about 27 days). Estimate Earth's mass using G = 6.67 x 10^-11 N m^2 kg^-2.

    • about 5.8 x 10^24 kg
    • about 2.0 x 10^30 kg
    • about 7.3 x 10^22 kg
    • about 6.0 x 10^22 kg

  12. Why does a satellite in a lower orbit travel faster?

    • The satellite loses mass as it falls towards the planet, which lets it travel faster.
    • The air at lower altitudes pushes the satellite along faster, which is why it speeds up.
    • Lower orbits give the satellite a larger mass, so its inertia makes it travel faster.
    • Gravity is stronger closer in, so a higher speed is needed for a stable orbit.

  13. Why does a low Earth orbit satellite gradually lose height over time?

    • The satellite's mass increases over time, pulling it inwards towards the planet's surface.
    • Residual drag removes energy, so the radius shrinks and the speed rises.
    • The satellite cools and contracts over time, which shrinks its orbit slowly.
    • Gravity becomes weaker with time, so the satellite gradually falls out of its orbit.

  14. What happens to the kinetic energy of a satellite when its orbital radius doubles?

    • It stays the same.
    • It quarters.
    • It halves.
    • It doubles.

  15. Two satellites have orbital radii r and 4r about the same planet, with equal masses. What is the ratio of the gravitational forces on them?

    • 1/4
    • 1/16
    • 1/2
    • 1/8

  16. Which statement about geostationary orbits is correct?

    • They are at the same height as the Moon's orbit.
    • They lie in the equatorial plane with a period matching Earth's rotation.
    • They lie over the poles with a period of 12 hours.
    • They have a period of one year exactly.

  17. Why does an orbit of a given radius have a fixed speed, independent of the satellite's mass?

    • The satellite's mass is always equal to the planet's mass in any stable circular orbit.
    • Both forces scale with the satellite's mass, so the mass cancels out.
    • Mass has no effect on any physical quantity in orbit, so it can be ignored entirely.
    • Heavier satellites always travel more slowly than lighter ones in the same orbit.

  18. Which quantity does NOT depend on the satellite's mass in a circular orbit of a given radius?

    • Gravitational force on the satellite
    • Orbital speed
    • Kinetic energy of the satellite
    • Momentum of the satellite

  19. A satellite orbits at radius 4.0 x 10^7 m about a planet with GM = 4.0 x 10^14 m^3 s^-2. What is its orbital speed?

    • 1.0 x 10^4 m s^-1
    • 3.2 x 10^3 m s^-1
    • 1.6 x 10^3 m s^-1
    • 6.3 x 10^3 m s^-1

  20. Satellite A has an orbital period twice that of satellite B about the same planet. What is the ratio r_A / r_B of their orbital radii?

    • 2.0
    • about 1.6
    • about 4.0
    • 0.5

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