How long will it take for a 60 kW crane to lift 2 tons of bricks to a height of 20 m?

N = 60 kW = 60 * 10 ^ 3 W.

m = 2 t = 2 * 10 ^ 3 kg.

g = 10 N / kg.

h = 20 m.

t -?

The power of the crane N is called a scalar physical quantity that shows how quickly the mechanical work A. The power of the crane N is determined by the formula: N = A / t, where A is the mechanical work performed by the crane when lifting the load, t is the time of lifting the load.

The operating time of the crane t will be the ratio: t = A / N.

With a uniform lifting of a load of mass m to a height h by a crane, the mechanical work of crane A will be expressed by the formula: A = m * g * h, where g is the acceleration of gravity.

The formula for determining the time of lifting the load t will take the form: t = m * g * h / N.

t = 2 * 10 ^ 3 kg g * 10 N / kg * 20 m / 60 * 10 ^ 3 W = 6.67 s.

Answer: the time for lifting the load by the crane is t = 6.67 s.