When resting, a person has a metabolic rate of about 3.0 105 joules per hour. the person is submerged neck-deep into a tub containing 1.21 103 kg of water at 19.30° c. if the heat from the person goes only into the water, find the water temperature after half an hour.

The temperature after half an hour is

Solution:

As per the question;

Metabolic rate of the person is 3.0105 J/h

Temperature, T =

Mass of the water,

Time duration, t = 0.5 h = 30 min = 180 s

Now,

Heat,

Thus heat transfer in half an hour:

Now, the temperature of water after half an hour, T' is given by:

where

s = 4186 J

he made 11 calls in one day

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.