An athlete is given 100 g of glucose $\left({\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\right)$ of energy equivalent to 1560 kJ. He utilizes 50 % of this gained energy in the event. In order to avoid storage of energy in the body, the weight of water he would need to perspire is : (The enthalpy of evaporation of water is 44 kJ/mole.)

As, athleter stilised 50% of the energy. Thus,

Utilised energy$=\frac{1560\times 50}{100}=780\mathrm{kJ}$

Remind energy is used in evaporation of water. Thus perspiration energy

= 1560 kJ - 780 kJ= 780 kJ

Also, 44 kJ energy used for evaporation of one mole (18 gram of H₂O) of water. Thus, 

 780 kJ energy utilised for evaporation of water,

$=\frac{780}{44}\times 18$

$=319 \mathrm{g}$