The Egyptians used "rollers (large logs) to help them move blocks up the ramps. Explain why this would have reduced the amount of work they had to do 2 A coal power station wastes 650 J out of every 1000 J of the coat's store of chemical energy. a Calculate the efficiency of the power station. Extension b The diagram shows the main steps in generating energy from coal In a power station. Suggest two steps where energy might be wasted, and for each step, suggest how the wasted energy is transferred. __

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The Egyptians used "rollers (large logs) to help them move blocks up the ramps. Explain why this would have reduced the amount of work they had to do 2 A coal power station wastes 650 J out of every 1000 J of the coat's store of chemical energy. a Calculate the efficiency of the power station. Extension b The diagram shows the main steps in generating energy from coal In a power station. Suggest two steps where energy might be wasted, and for each step, suggest how the wasted energy is transferred. __

Answer 1

1. By using rollers, the Egyptians reduced the friction between the blocks and the ground, thus reducing the amount of work they had to do. 2. a) Efficiency of the power station = (350 / 1000) * 100 = 35% or 0.35 (to 2 decimal places). 3. Extension: b) Two steps where energy might be wasted in a coal power station are during the combustion of coal and during the conversion of thermal energy into mechanical energy in the turbine. The wasted energy is transferred as light and sound during combustion and as heat to the surrounding environment during the conversion of thermal energy into mechanical energy.

Answer 2

## Step 1: The first part of the question is a conceptual question about physics. When the Egyptians used rollers or large logs to move blocks up the ramps, they were reducing the friction between the blocks and the ground. Friction is a force that resists the motion of objects. By reducing the friction, they were reducing the amount of force they had to apply to move the blocks, and hence reducing the amount of work they had to do. Work is defined as the force applied to an object times the distance the object moves, so if the force is reduced, the work is also reduced. ## Step 2: The second part of the question is about calculating the efficiency of a coal power station. The efficiency of a device is defined as the proportion of useful energy transferred by the device. It can be calculated as the ratio of useful output energy (or power, if the calculation is per unit time) to the total input energy (or power). ### The formula for efficiency is: **Efficiency = (Useful energy output / Total energy input) * 100%** In this question, the total input energy is 1000J and the wasted energy is 650J. The useful energy output can be calculated as the difference between the total input energy and the wasted energy. ## Step 3: The extension part of the question is about identifying steps in the energy generation process where energy might be wasted and how the wasted energy is transferred. In a coal power station, energy can be wasted in several steps. For example, during the combustion of coal, not all the chemical energy in the coal is converted into thermal energy. Some of the energy is lost as light and sound. Similarly, during the conversion of thermal energy into mechanical energy in the turbine, not all the thermal energy is converted into mechanical energy. Some of the energy is lost as heat to the surrounding environment.

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