ANSWER
45%
EXPLANATION
Given:
• The energy used by the electric motor, W_in = 80 J
,• The mass lifted, m = 1.8 kg
,• The distance the mass is lifted, d = 2 m
Find:
• The efficiency of the machine
The mechanical efficiency of a machine is defined as the quotient between the output work and the input work - usually multiplied by 100 to express it as a percentage,
[tex]efficiency=\frac{W_{out}}{W_{in}}\cdot100[/tex]In this case, the work done by the electric motor is 80 J - which is the input work. Let's find how much work is actually required to lift the mass,
[tex]W_{out}=F_g\cdot d=mgd=1.8kg\cdot10m/s^2\cdot2m=36J[/tex]So, the efficiency is,
[tex]efficiency=\frac{36J}{80J}\cdot100=0.45\cdot100=45\%[/tex]Hence, the efficiency of the machine is 45%.
