A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1m 1000 times. Assume…

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1m 1000 times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up? Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate. Take g=9.8 ms-2 :
  1. 9.89×10-3 kg
  2. 12.89×10-3 kg
  3. 2.45×10-3 kg
  4. 6.45×10-3 kg

Solution

m=10kg, h=1m, 1000 times

Work done against gravity mgh

=10×1×9.8=98 J

In lifting 1000 times

=1000×98

=9.8×104 J

Fat burn with 20% efficiency =3.8×107 J×0.2

=7.6×106 J per kg

m=9.8×1047.6×106=1.289×10-2

=12.89×10-3 kg

Asked in: JEE Main 2016 (03 Apr)

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