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Applying Kick's law with a constant of \( 8 \) kWh per tonne, reducing from \( 20 \) mm to \( 5 \) mm requires

  • A.11.1 kWh per tonne
  • B.8.0 kWh per tonne
  • C.32.0 kWh per tonne
  • D.2.0 kWh per tonne

Answer: A

Correct answer: 11.1 kWh per tonne

Kick's law makes the energy depend on the ratio of sizes rather than on their absolute values:

\[ E = K_K \ln \frac{x_1}{x_2} = 8 \ln \frac{20}{5} = 8 \ln 4 = 8 \times 1.386 = 11.1\ \mathrm{kWh/tonne} \]

Because only the ratio enters, Kick's law predicts the same energy for 20 mm to 5 mm as for 4 mm to 1 mm - which is why it describes coarse crushing well and fine grinding badly, where Rittinger's surface-based law fits better.

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