Question

How much metres can a 50 kg man climbs by using the energy from a slice of a bread which produces 420 kJ heat? Assuming that the human body effciency working is `30%`. Use `g=10 m//s^(2)`.

Answer 1

Let h be the height climbed by man.
increase in PE of man = `mgh = 50 xx 10 xx h j`
Heat produced , `H = 420 xx 1000 j`
`=4.2 xx 10^(5) J`
effciency of man = `30%`, so heat energy utilized by man in doing work is
`=30/100 xx 4.2 xx 10^(5) = 12.6 xx 10^(4) J`
Now, increase in PE = heat energy utilized
`50 xx 10 xx h = 12.6 xx 10^(4)`
or `h=(12.6 xx 10^(4))/(50 xx 10) = 252 m`.