By the definition, power is work performed at a time unit (work divided by time). Therefore in this problem the total work done is where
is the given power and
is the given time.
Also it is known that the amount of work performed on a body adds to its total energy. The total energy of the sacks consists of the kinetic energy and the potential energy
So
because the initial speed is probably zero. Here
is the height in question and
is the end speed.
To maximize we need to minimize
and its minimum is zero. In this case
and
Two sacks have total mass of
Thus the numerical answer is about
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