To solve this problem it is necessary to apply the concepts related to work and power.
Remember that work is defined as the force applied on a body - or exerted by it - to travel a certain distance, and that the power is that energy mentioned to perform that activity in a given instance of time.
Mathematically work is defined as
[tex]W = Fd[/tex]
Where
[tex]F = Force \rightarrow mass*acceleration[/tex]
d = Distance
At this case the acceleration is the same that gravitational acceleration
At the same time we have that power is defined as
[tex]P = \frac{W}{\Delta t}[/tex]
Replacing our values we have that the Work done was
[tex]W = mg*d[/tex]
[tex]W = (20)(9.81)(2)[/tex]
[tex]W = 392.4J[/tex]
Now substituting this value at the Power equation we have
[tex]P = \frac{392.4J}{4s}[/tex]
[tex]P = 100W[/tex]
Therefore the power that she is supplying is 100W.
