A load weighing 7 tons is lifted from the Mine at a constant speed of 3 m / s.

A load weighing 7 tons is lifted from the Mine at a constant speed of 3 m / s. What is the efficiency of the crane. If its power is 250 kW?

Initial data: m (cargo weight) = 7 t; V (constant speed of lifting the load) = 3 m / s; Nk (crane power) = 250 kW = 250 * 10 ^ 3 W.

Reference values: g (acceleration due to gravity) = 10 m / s ^ 2

SI system: m = 7 t = 7 * 10 ^ 3 kg.

The efficiency of the crane is calculated by the formula: η = Nп / Nз = F * V / Nк = m * g * V / Nк.

Let’s calculate: η = 7 * 10 ^ 3 * 10 * 3 / (250 * 10 ^ 3) = 0.84 or 84%.

Answer: The efficiency of the crane is 84%.