A large stone is lifted from the ground and placed on a high shelf. Explain the energy transfers that take place during this process, and state what happens to the total energy of the stone and its surroundings.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A builder lifts a 15 kg stone from the ground and places it on a shelf 2 m above the floor. The builder's muscles do work to raise the stone.
Model answer (5 marks)
Work is done on the stone because a force moves it through a distance.
Chemical energy in the builder's muscles is transferred to the stone.
The stone gains gravitational potential energy as it is raised to a higher height.
Some of the energy is lost as thermal energy/heat due to friction and the heat generated in the muscles.
The total energy of the stone and its surroundings remains unchanged, in accordance with the conservation of energy.
Chemical energy in the builder's muscles is transferred to the stone.
The stone gains gravitational potential energy as it is raised to a higher height.
Some of the energy is lost as thermal energy/heat due to friction and the heat generated in the muscles.
The total energy of the stone and its surroundings remains unchanged, in accordance with the conservation of energy.
Examiner tips
- Use the word "work" and explain it as force × distance. Mention the source of energy (chemical in muscles) and the type of energy gained by the stone (gravitational potential). Include the loss to heat. State the conservation of energy conclusion.
Common mistakes
- Forgetting to mention the chemical energy source. Saying the stone’s energy increases without noting the loss to heat. Using vague terms like "energy" without specifying types.
Mark scheme (5 marks)
- Work is done on the stone because a force moves it through a distance
- Chemical energy (in the builder's muscles) is transferred
- The stone gains gravitational potential energy because it is raised to a greater height
- Some energy is wasted, transferred to the surroundings as thermal energy / heat (due to friction or heat generated in muscles)
- The total energy of the stone and its surroundings remains the same, in accordance with the conservation of energy
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Energy concepts questions
- A small toy car is wound up by compressing a spring inside it. When released on …
- A cyclist rides along a flat road at a constant speed. The cyclist's legs apply …
- A roller coaster car starts from rest at the top of a tall hill and rolls down t…
- A student uses an electric fan heater to warm a room. Describe the useful energy…