Question

A student eats a dinner containing 2000Calories of energy. He wishes to do an equivalent amount of work in the gymnasium by lifting a 10Kg object. How many times must he raise the object to expand this much work? Assume that he lies to his back and raises it a distance of 0.5m each, and the effort done to let the weight down is 50% of the effort done to raise it.

Answer 1

$E = 2000\ cal$

$E\approx 2000*4.2=8400\ J$

$m= 10kg$

$g = 9.8\frac{m}{s^2}$

$h =0.5\ m$

$\text{Energy for one lift in and one lowering of the weight:}$

$E_1= mgh +0.5mgh =1.5mgh$

$E_1= 1.5*10*9.8*0.5=73.5\ J$

$n =\lceil \frac{E}{E_1}\rceil= \lceil \frac{8400}{73.5}\rceil=115$

$\text{Answer: }115$