Arthur Clarke wrote an interesting short story called “A Slight Case of Sunstroke.” Disgruntled football fans came to the stadium one day equipped with mirrors and were ready to barbecue the referee if he; favored one team over the other. Imagine the referee to be a cylinder filled with water of mass 60.0 kg at 35.0°C. Also imagine that this cylinder absorbs all the light reflected on it from 50,000 mirrors. If the heat capacity of water is 4.20 . 103 J/(kg°C), how long will it take to raise the temperature of the water to 100 °C? Assume that the Sun gives out 1.00 . 103 W/m2, the dimensions of each mirror are 25.0 cm by 25.0 cm, and the mirrors are held at an angle of 45.0°.
THINK:
The time taken to raise the temperature of the water in the cylinder to
will depend on the total power reflected by the mirrors and the heat energy absorbed by the water in the cylinder. The amount of the power reflected by the mirrors depends on the intensity of solar radiation, and effective area. The absorbed heat energy of water will depend on the mass of the water, specific heat capacity and the temperature difference.
SKETCH:
The sketch for the given problem is shown in the below figure.
RESEARCH:
The amount of power reflected by mirror is given by the equation
Here, the intensity of the solar radiation,
From the above diagram, the effective area is given by
Here, the area of the mirror,

The angle of the mirror with the horizontal,
Therefore, the power reflected by the mirror becomes as
Now, the total power reflected by all the mirrors is
Here, the number of the mirrors, 
The heat energy required to increase the water temperature to
is given by the equation
Here the mass of the water,
The specific heat of the water,
The initial temperature of the water,
SIMLIFY:
Therefore, the time taken to raise the temperature of the water is given by
…… (1)
CALCULATE:
Now, substituting the numerical values in the equation (1), we get ‘
’