The total distance covered by the person is 12 times the height of each stair: [tex]\Delta h=12 \cdot 30 cm=360 cm=3.60 m[/tex]
The work done by the person to climb the stairs is equal to the increase in his gravitational potential energy: [tex]W= \Delta U=mg \Delta h=(45 kg)(9.81 m/s^2)(3.60 m)=1589.2 J[/tex]
And therefore, the power generated by the person in 12 s is the work done divided by the time taken: [tex]P= \frac{W}{t}= \frac{1589.2 J}{12 s}=132.3 W [/tex]
