What is the efficiency of an excavator with a 5 kW engine if it lifts 144 tons of sand to a height of 10 m in 2 hours?

Initial data: Ns (excavator engine power) = 5 kW (5 * 10 ^ 3 W); m (mass of the raised sand) = 144 tons (144 * 10 ^ 3 kg); h (sand lifting height) = 10 m; t (duration of excavator operation) = 2 hours (7200 s).

Reference values: ρp (bulk density of sand) = 1500 kg / m3; by condition g (acceleration of gravity) = 10 m / s2.

The efficiency of the excavator is determined by the formula: η = Np / Nz = (A / t) / Nz = ΔEp / (Nz * t) = m * g * h / (Nz * t).

Calculation: η = 144 * 10 ^ 3 * 10 * 10 / (5 * 10 ^ 3 * 7200) = 0.4 (40%).