Student Activity
Gravity's Big Reach!: Answer Key


Copy Master

  1. Use the graph provided to determine the local gravitational field strength on the Earth's surface (radius 6.4 x 103 km).

    ANS: 9.8 N/kg

  2. Use the graph provided to determine the local acceleration (due to gravity) on the Earth's surface (radius 6.4 x 103 km).

    ANS: 9.8 m/s2

  3. Use the graph provided to determine the local gravitational field strength on the Earth's surface if the Earth's radius were to mysteriously increase to 1.0 x 104 km).

    ANS: 3.9 N/kg

  4. Use the graph provided to determine the local acceleration (due to gravity) on the Earth's surface if the Earth's radius were to mysteriously increase to 1.0 x 104 km).

    ANS: 3.9 m/s2

  5. Use the graph provided to determine the local gravitational field strength on the Earth's surface if the Earth's radius were to mysteriously decrease to 5.0 x 103 km).

    ANS: 15.2 N/kg

  6. Use the graph provided to determine the local acceleration (due to gravity) on the Earth's surface if the Earth's radius were to mysteriously decrease to 5.0 x 103 km).

    ANS: 15.2 m/s2

  7. Show by dimensional analysis that N/kg is dimensionally the same as m/s2.

    ANS: a newton is a unit of force i.e. mass x acceleration
    dimensionally N = kg·m/s2
    therefore N/kg =(kg·m/s2)/kg = m/s2

    Q.E.D.

  8. Using the expression

    gm = GMe /rm2

    Determine the acceleration of the moon gm towards the Earth (mass Me) and where rm is the mean distance to the Moon.

    ANS: 2.75 x 10-3 m/s2

  9. Calculate the local gravitational acceleration on the surface of the Moon due to the Moon's mass.

    ANS: 1.71 m/s2

  10. Calculate the local gravitational acceleration on the surface of Mars due to its mass.

    ANS: 3.69 m/s2

G = 6.67 x 10-11 Nm2/kg2
rm = 3.8 x 108 m (variable due to the eccentricity of the Moon's orbit)
Me = 5.97 x 1024 kg
Mass of the Moon = 7.16 x 1022 kg
Radius of the Moon =1.74 x 106 m
Mass of Mars = 6.35 x 1023 kg
Radius of Mars = 3.40 x 106 m

Home | Information for Teachers | Gravity | Escape to Infinity | Low Earth Orbit | Ground Tracks | Geosynchronous Satellites | Conic Sections | Energy | Manoeuvring in Space

Prepared by YES I Can! Science