A man consumes 2055 kcal of food in one day, converting most of it to body temperature. If he loses half this energy by evaporating water (through breathing and sweating), how many kilograms of water evaporate?

1.903 kg.

Explanation:

Energy obtained from the food, Q= 2055kCal

Half of the energy lost to evaporating water = 2055/2

= 1027.5 kCal

Latent heat of water, L = 540 kCal/kg

Q= m × L

m = 1027.5/540

= 1.903 kg.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.