Question

A 790N person runs up a flight of 40 stairs (.25m for each step) in 20 seconds, and then down 10 steps in 5 seconds. How much total mechanical work is completed? How much total mechanical power is generated? Show all work.

Answer 1

A person runs up 40 stairs and then come down 10 steps

So total stairs upwards is given as

$N = 40 - 10 = 30$

now here we will have total height reached

$H = N\times h$

$H = 30 \times 0.25 = 7.5 m$

Now total energy used or mechanical work done is

$W = mgH$

$W = 790 \times 7.5 = 5925 J$

Now the mechanical power is given as

$P = \frac{W}{t}$

$P = \frac{5925}{20+ 5} = 237 W$