# The tower crane evenly lifts a load weighing 380 kg to a height of 22m in 100s.

**The tower crane evenly lifts a load weighing 380 kg to a height of 22m in 100s. Determine the current in the electric motor at a voltage of 220V, if it is known that the efficiency of the crane electric motor is 38%**

m = 380 kg.

g = 9.8 m / s2.

h = 22 m.

t = 100 s.

U = 220 V.

Efficiency = 38%.

I -?

Efficiency = 38% means that only 38% of the electric motor energy goes to lifting the load.

Efficiency = Apol * 100% / Azat.

The useful work of Apol is expressed by the formula: Apol = m * g * h.

The spent work Azat is expressed by the formula of the Joule-Lenz law: Azat = I * U * t.

Efficiency = m * g * h * 100% / I * U * t.

The formula for determining the current strength I in the electric motor of a tower crane will be: I = m * g * h * 100% / efficiency * U * t.

I = 380 kg * 9.8 m / s2 * 22 m * 100% / 38% * 220 V * 100 s = 9.8 A.

Answer: the current in the electric motor is I = 9.8 A.