JEE Main | 2016Work, Power and EnergyEasy

Question

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 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 X 10 7 J of energy per kg
which is converted to mechanical energy with a 20 % efficiency rate. Take g = 9.8 ms-2 :

Options

A.

 6.45 X10-3 kg 

B.

9.89 x 10-3 kg

C.

12.89 x 10 -3 kg 

D.

2.45 x10 -3 kg

Solution

Let fat used be ‘x’ kg
⇒Mechanical energy available = x ×3.8×10 7 ×20100
Work done in lifting up = 10× 9.8 ×1000
⇒X×3.8×107×20100=9.8×104⇒X≈12.89×10-3 kg.

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