# The student lifted a weight of 0.4 kg using a lever to a height of 5 cm, applying a force of 1 N.

**The student lifted a weight of 0.4 kg using a lever to a height of 5 cm, applying a force of 1 N. At the same time, the end of the lever, which was pressed by the student, moved 21 cm. Determine the efficiency of this lever.**

m = 0.4 kg.

h = 5 cm = 0.05 m.

F = 1 N.

s = 21 cm = 0.21 m.

g = 9.8 m / s ^ 2.

Efficiency -?

The efficiency is determined by the formula: efficiency = Apol * 100% / Azat, where Apol is useful work, Azat is work expended.

The useful work of Apol is the work of lifting a load to a height, expressed by the formula: Apol = m * g * h.

The spent work Azat is the work that the boy performed, expressed by the formula: Azat = F * s.

Efficiency = m * g * h * 100% / F * s.

Efficiency = 0.4 kg * 9.8 m / s ^ 2 * 0.05 m * 100% / 1 N * 0.21 m = 93.3%.

Answer: the efficiency of the lever efficiency = 93.3%.