The power expended is 500 W
Explanation:
First of all, we start by calculating the work done by the man in order to ascend: this is equal to the gravitational potential energy gained by the man, which is

where
m = 50 kg is the mass of the man
is the acceleration of gravity
is the change in height
Substituting,

Now we can calculate the power expended, which is given by

where
W = 2500 J is the work done
t = 5 s is the time elapsed
Substituting, we find

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