A competitor carries two very heavy sleds across level ground at a steady height. How much work does he do on the sleds?

1. Everyday language would call carrying heavy sleds very hard work. 2. In physics the test is whether the force has a part along the displacement. 3. His force on the sleds points straight up to balance gravity, while the sleds move sideways. 4. There is no part of his force along the displacement, so he does no work on the sleds. 5. His muscles do use energy to keep the force going, but that energy is not transferred to the sleds, so the answer is not a lot of work. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 5: Work, energy and power_