OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(b) gravitational potential energy of an object in a uniform gravitational…
Full specification wording
Kinetic and potential energies: (b) gravitational potential energy of an object in a uniform gravitational field; E p = mgh
Gravitational potential energy (GPE) is the energy an object possesses due to its position in a gravitational field.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 2 of 3
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Gravitational potential energy (GPE) is the energy an object possesses due to its position in a gravitational field. In a uniform gravitational field, such as near the Earth's surface, the change in GPE when an object of mass m is raised by a height h is given by Ep = mgh, where g is the gravitational field strength (approximately 9.81 N kg⁻¹ on Earth). The equation assumes the field is uniform, meaning g is constant over the height moved. The unit of GPE is the joule (J).
For example: Lifting a 2 kg mass by 3 m gives Ep = 2 × 9.81 × 3 = 58.86 J. In MCQ questions, you may calculate GPE, compare changes, or identify the effect of changing mass, height, or gravitational field strength.
What earns the marks
- Gravitational potential energy is the energy stored in an object due to its position in a gravitational field.
- In a uniform gravitational field, the change in gravitational potential energy is calculated using Ep = mgh.
- m is mass in kg, g is gravitational field strength in N kg⁻¹, and h is vertical height change in m.
- The unit of gravitational potential energy is the joule (J).
- The equation applies when the gravitational field is uniform, i.e., g is constant over the change in height.
Common mistakes and how to put them right
Using the wrong value for g.
Put it right: Check the question for the value of g to use; if not given, use 9.81 N kg⁻¹.
Forgetting that h is the vertical height change, not the distance moved along a slope.
Put it right: Use the vertical component of displacement.
Mixing up mass and weight.
Put it right: Ensure you use mass in kg, not weight in N.
Assuming the equation applies in non-uniform fields.
Put it right: For large height changes, g varies and the equation is not accurate.
Exam tips
- In multiple-choice questions, check whether the height is vertical; if an object moves along a slope, you must use the vertical height, not the slope length.
- If the question gives g as 10 N kg⁻¹, use that value; otherwise use 9.81 N kg⁻¹.
- Remember that gravitational potential energy is relative to a chosen zero level; the equation gives the change in GPE.
Try the lesson
The start of the Kinetic and potential energies: (b) gravitational potential energy of an object in a uniform gravitational field; E p = mgh lesson, made from checked teaching notes for this specification point.
Listen
Gravitational potential energy (GPE) is the energy an object possesses due to its position in a gravitational field. In a uniform gravitational field, such as near the Earth's surface, the change in GPE when an object of mass m is raised by a height h is given by Ep = mgh, where g is the gravitational field strength (approximately 9.81 N kg⁻¹ on Earth). The equation assumes the field is uniform, meaning g is constant over the height moved. The unit of GPE is the joule (J). For example, lifting a 2 kg mass by 3 m gives Ep = 2 × 9.81 × 3 = 58.86 J. In MCQ questions, you may calculate GPE, compare changes, or identify the effect of changing mass, height, or gravitational field strength. A strong answer earns marks for these points. Gravitational potential energy is the energy stored in an object due to its position in a gravitational field. In a uniform gravitational field, the change in gravitational potential energy is calculated using Ep = mgh. m is mass in kg, g is gravitational field strength in N kg⁻¹, and h is vertical height change in m. The unit of gravitational potential energy is the joule (J). A common slip: Using the wrong value for g: for example, using 10 m s⁻² instead of 9.81 N kg⁻¹ when the question expects the standard value. Instead, check the question for the value of g to use; if not given, use 9.81 N kg⁻¹. Exam tip: In multiple-choice questions, check whether the height is vertical; if an object moves along a slope, you must use the vertical height, not the slope length.
See it
Key words
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Gravitational potential energy
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Uniform gravitational field
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Gravitational field strength
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Ep = mgh
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See every definition
- Gravitational potential energy
- The energy an object possesses due to its position in a gravitational field, measured in the joule (J).
- Uniform gravitational field
- A field in which g is constant over the height moved, such as near the Earth's surface.
- Gravitational field strength
- The quantity g in the equation Ep = mgh, approximately 9.81 N kg⁻¹ on Earth.
- Ep = mgh
- The equation giving the change in gravitational potential energy when an object of mass m is raised by a height h in a uniform gravitational field.
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