Se dă:
η=70%
h=2 m
F=420 N
m - ?
η=Lu/Lt·100%
Lu=m·g·h
Lt=F·l
η=(m·g·h)/(F·l)·100%=(m·g)/F·100%
(m·10 N/kg)/420 N·100%=70%
(m·10 N/kg)/420 N=70%/100%
(m·10 N/kg)/420 N=0,7
m·10 N/kg=F/0,7
m·10 N/kg=420 N/0,7
m·10 N/kg=600
m=600/g
m=600/10 N/kg
m=60 kg
Răspuns: Masa corpului este de 60 kilograme.