Answer:
79.8 %
Explanation:
The energy in input to the system is equal to the work done by the worker, so:
[tex]E_{in} = Fd[/tex]
where
F = 129 N is the force applied
d = 16.5 m is the displacement of the rope
Substituting,
[tex]W_{in} = (129)(33)=4257 J[/tex]
The output work of the system is the gravitational potential energy gained by the crate, so
[tex]W_{out} = mg \Delta h[/tex]
where
m = 33 kg is the mass of the crate
g = 9.8 m/s^2 is the acceleration of gravity
[tex]\Delta h =16.5 m[/tex] is the gain in height of the crate
Substituting,
[tex]W_{out}= (33)(9.8)(16.5)=5336 J[/tex]
So, the efficiency of the pulley is
[tex]\eta = \frac{W_{in}}{W_{out}}=\frac{4257}{5336}=0.798[/tex]
So, 79.8 %.
