A person runs up 40 stairs and then come down 10 steps
So total stairs upwards is given as
[tex]N = 40 - 10 = 30[/tex]
now here we will have total height reached
[tex]H = N\times h[/tex]
[tex]H = 30 \times 0.25 = 7.5 m[/tex]
Now total energy used or mechanical work done is
[tex]W = mgH[/tex]
[tex]W = 790 \times 7.5 = 5925 J[/tex]
Now the mechanical power is given as
[tex]P = \frac{W}{t}[/tex]
[tex]P = \frac{5925}{20+ 5} = 237 W[/tex]
