A person trying to lose weight (dieter ) lifts a 10 kg mass through 0.5m, 1000 times, A ssume that the potential energy lost each time she lowers the mass is dissipated (a) How much work does she does against the gravitational force ? (b) Fat supplies `3.8xx10^(7) J` of energy per kilogram which is converted to mechanical energy with a `20%` efficiency rate. How much fat will the dieter use up ?

Explanation

m = 10 kg , h = 0.5 m , n = 1,000
(a) Work done by the dieter against gravitational force = n (mgh)
(b) Mechanical enery supplied by 1 kg of fat
` = 20/100 (3.8 xx10^(7))`
`= 0.76 xx10^(7)` J/kg
Fat used by dieter = `(1kg)/(0.76 xx10^(7))xx 49,000`
` = 64473.6 xx10^(-7)`
` = 6.44 xx10^(3) ` kg