6.22 A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the mass is dissipated.
(a) How much work does she do against the gravitational force ?
(b) Fat supplies 3.8 × 107J of energy per kilogram which is converted to mechanical energy with a 20% efficiency rate. How much fat will the dieter use up?
6.22 A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the mass is dissipated.
(a) How much work does she do against the gravitational force ?
(b) Fat supplies 3.8 × 107J of energy per kilogram which is converted to mechanical energy with a 20% efficiency rate. How much fat will the dieter use up?
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1 Answer
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6.22 Mass lifted, m = 10 kg
Height to which the mass lifted, h = 0.5 m
No of repetitions, n = 1000
(a) Work done against gravitational force,
W = nmgh = 1000 49050 J
(b) Mechanical energy supplied by 1 kg fat, with 20% efficiency rate = 0.2 3.8 = 0.76 J/kg
Fat used by dieter = 49050 / (0.76 kg = kg
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