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

Here, m = 10kg, h=0.5 m, n=1000
a) work done against graviational force.
`w=n(mgH) = 1000xx (10 xx 9.8 xx 0.5)`= 49000 J
b) Mechanical energy supplied by 1kg of fat `= 3.8 xx 10^(7) xx 20//100`
`=0.76 xx 10^(7)J//kg`
`therefore` Fat used by the dieter = 1kg`(0.76 xx 10^(7) xx 49000 = 6.45 xx 10^(-3)kg`