JEE Main Physics question
A person trying to lose weight by burning fat lifts a mass of 15 kg up to a height of 2 m, 500 times. Assume that the potential energy lost each time he lowers the mass is dissipated. Fat supplies 3.8×10⁷ J of energy per kg which is converted to mechanical energy with a 15% efficiency rate. The fat he will use up considering the work done only when the weight is lifted up is ×10⁻² kg. (Take g = 10 m/s²) [JEE Main 2011]
Answer: 2.63
Solution
Total work done in lifting the mass = (15×10×2)×500 = 1.5×10⁵ J. The useful mechanical energy obtained per kg of fat, at 15% efficiency, is 3.8×10⁷ × 0.15 =
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