A student wants to estimate the gravitational potential energy stored in a full can of fizzy drink when it is placed on a shelf. Explain how the student could arrive at a reasonable estimate, including a final numerical estimate with appropriate units.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
GPE = mgh
The student can estimate the mass of a full can of drink by assuming a typical 330 ml can.
* Mass of the can: 0.33–0.40 kg (≈0.35 kg is a reasonable value).
* Height of the shelf: 0.5–2.0 m (≈1.0 m is a typical shelf height).
Using g = 10 N kg⁻¹ (or 9.8 N kg⁻¹) the calculation is:
GPE = 0.35 kg × 10 N kg⁻¹ × 1.0 m = 3.5 J
Thus the gravitational potential energy stored in the can on the shelf is about 3–4 J.
This estimate falls within the expected range of 0.5–8 J for sensible values of mass and height.
The student can estimate the mass of a full can of drink by assuming a typical 330 ml can.
* Mass of the can: 0.33–0.40 kg (≈0.35 kg is a reasonable value).
* Height of the shelf: 0.5–2.0 m (≈1.0 m is a typical shelf height).
Using g = 10 N kg⁻¹ (or 9.8 N kg⁻¹) the calculation is:
GPE = 0.35 kg × 10 N kg⁻¹ × 1.0 m = 3.5 J
Thus the gravitational potential energy stored in the can on the shelf is about 3–4 J.
This estimate falls within the expected range of 0.5–8 J for sensible values of mass and height.
Examiner tips
- State the formula GPE = mgh explicitly. Use realistic estimates for m and h and show the calculation. Give the final answer in joules, including the unit.
- common_mistakes
- :
- Using the wrong unit for g (e.g. 9.8 m s⁻² instead of 9.8 N kg⁻¹). Failing to include the unit in the final answer. Choosing unrealistic values for mass or height that give an answer outside the 0.5–8 J range.
Mark scheme (5 marks)
- Identifies that gravitational potential energy = mass × gravitational field strength × height (GPE = mgh)
- Gives a reasonable estimate for the mass of a full can of drink (approximately 0.33–0.40 kg)
- Gives a reasonable estimate for the height of the shelf above the floor (approximately 0.5–2.0 m)
- Uses g = 10 N/kg (or 9.8 N/kg) correctly in their calculation
- Arrives at a final numerical estimate consistent with their chosen values, stated in joules (approximately 0.5–8 J for sensible inputs)
Key terms in this question
gravitational potential energy
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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