Physics · OCR H556 · Topic 5.4

Gravitational fields

Point and spherical masses, Newton's law of gravitation, planetary motion, gravitational potential and energy.

  • 4 sub-topics
  • Taught in Year 13
  • 38 practice questions
  • 4 animated lessons
Practice questions (38) Lessons Worksheets coming soon All OCR Physics topics

What the specification says

Every sub-topic OCR can examine in this topic, with its reference number from the official specification. The Y12 and Y13 tags show when each sub-topic is usually taught.

  1. 5.4.1Point and spherical massesY13
  2. 5.4.2Newton's law of gravitationY13
  3. 5.4.3Planetary motionY13
  4. 5.4.4Gravitational potential and energyY13

Try 3 questions

Easy, medium and hard questions from this topic, each with a worked solutions and the mark for every step. All 38 questions in this topic, free, no account needed.

Electric and magnetic fields

Not needed for Year 12Easy

Electric fields · Year 13 · 3 marks

A small positive test charge is placed near a charged sphere.
  1. (a)
    Define an electric field.
    (1)
  2. (b)
    Describe the field lines around an isolated positive point charge.
    (2)
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Part (a)1 mark

  1. A region in which a charged particle experiences a force.

Part (b)2 marks

  1. Radial, pointing outwards,
  2. closer together nearer the charge (the field is stronger).

Total3

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  • A
  • B
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Gravitational fields

Not needed for Year 12Medium

Gravitational field strength · Year 13 · 3 marks

The Moon has mass 7.3×10227.3 \times 10^{22} kg and radius 1.7×1061.7 \times 10^{6} m.
  1. (a)
    Calculate the gravitational field strength at the surface of the Moon.
    (2)
  2. (b)
    Calculate the field strength at a height equal to one radius above the surface.
    (1)

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Part (a)2 marks

  1. g=GMr2g = \frac{GM}{r^2}
  2. g=1.68 N kg−1g = 1.68\ \mathrm{N\,kg^{-1}}

Part (b)1 mark

  1. g=0.421 N kg−1g = 0.421\ \mathrm{N\,kg^{-1}}

Total3

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Fields and their consequences

Not needed for Year 12Hard

Gravitational potential · Year 13 · 5 marks

A satellite of mass 1200 kg is moved from the Earth's surface (radius 6.4 × 10⁶ m, Earth mass 6.0 × 10²⁴ kg) to a height of 4.0×1054.0 \times 10^{5} m.
  1. (a)
    Calculate the gravitational potential at the surface and at the new height.
    (2)
  2. (b)
    Calculate the work done to move the satellite.
    (2)
  3. (c)
    Explain why gravitational potential is always negative.
    (1)

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Part (a)2 marks

  1. V1V_1=−6.25×107 J kg−1{}= -6.25 \times 10^{7}\ \mathrm{J\,kg^{-1}}
  2. V2V_2=−5.89×107 J kg−1{}= -5.89 \times 10^{7}\ \mathrm{J\,kg^{-1}}

Part (b)2 marks

  1. W=mΔVW = m\Delta V
  2. W=4.41×109 JW = 4.41 \times 10^{9}\ \mathrm{J}

Part (c)1 mark

  1. Zero is at infinity, and work must be done to move a mass out to infinity.

Total5

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  • B
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