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Maize energy transfer area calculation
Farmers can increase the growth rate of farm animals by controlling the animals' diets. A farmer has 1000 chickens.
- The farmer feeds the chickens on seeds from maize plants.
- 1 hectare of land produces 16.4 tonnes of maize seeds.
- The maize seeds have an energy content of 16 MJ per kg.
- Chickens can use 80% of the energy in maize seeds.
- Each chicken needs 46 MJ of energy to grow to full size.
Calculate the area of land needed to provide enough energy from maize seeds for 1000 chickens to grow to full size. Give your answer in m². Give your answer to 3 significant figures.
- 1 hectare
- 10 000 m²
- 1 tonne
- 1000 kg
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Marking points
- 1 Correctly begins the energy/mass conversion, such as 1000 × 46 = 46 000 MJ or 16.4 tonnes = 16 400 kg.
- 2 Determines the total energy per hectare before efficiency or an equivalent linked step.
- 3 Correctly applies the 80% usable-energy factor.
- 4 Converts the required proportion of a hectare into about 2191.3 m².
- 5 Rounds the final area to 2190 m² (3 significant figures).
Full-mark answer
Energy needed = 1000 × 46 = 46 000 MJ. One hectare produces 16.4 × 1000 = 16 400 kg, containing 16 400 × 16 = 262 400 MJ; usable energy = 0.80 × 262 400 = 209 920 MJ per hectare. Area = (46 000 ÷ 209 920) × 10 000 = 2191.3 m², which is 2190 m² to 3 significant figures.
Why this answer loses marks
Use the maize energy per hectare without applying the usable-energy percentage.
This overstates the energy available to the chickens; apply the efficiency before scaling the land area and rounding.