Well, we usually assume that the resistance of a circuit component
is constant and doesn't change. But the truth is that for anything
that conducts current, its resistance always increases somewhat
when it warms up.
For things like light bulbs, electric toasters, space heaters, electric
stove burners, the heat coils in a blow-dryer ... anything that's
designed to be really hot when it's doing its job ... the resistance
of those things increases significantly when they come up to their
operating temperatures.
A. IMA: 4
The Ideal Mechanical Advantage (IMA) is given by:
where
is the input distance
is the output distance
For the pulley system in this problem, 
and 
, so the IMA is
B. MA: 3.59
The actual mechanical advantage (AMA), or simply the Mechanical Advantage (MA), is given by
where 
is the output force and 
is the input force. For the pulley system in this problem, 
and 
, so the MA is
C. Efficiency: 89.8 %
The efficiency of a machine is equal to the ratio between the MA and the AMA:
Therefore, in this case,
