Like the precise measurements in science are required, reasonable approximations of physical quantities using rudimentary ideas and general observations are equally valuable.
a) \text{ Density } = \frac{\text{ mass }}{\text{ volume }}
Total mass of rain fall can be determined with knowledge of rainfall volume and water density.
Density of water = 10^{3} kgm^{-3}
During the monsoon, the height of the water is measured h = 215 cm = 2.15 m
Area of the earth A = 3.3 * 10^{12} m^2
Volume of the rain fall = Ah = 3.3 * 10^{12} m^2 * 2.15 m
= 7.1 * 10^{12} m^3
Total mass of rain fall = \text{ Density * volume } = 10^{3} kgm^{-3} * 7.1 * 10^{12} m^3
= 7.1 * 10^{15} kg
b)We can estimate the mass of the elephant mass using the Archimedes principle
As per the Archimedes principle, the upward buoyant force exerted on a body immersed in a fluid, whether partially or completely submerged, is equivalent to the weight of the fluid that the body displaces.
Displaced water mass =(displaced water volume)x (density of water)
When elephant is immersed in water, measure the volume of water displaced = V
Displaced water mass = V *10^{3} kgm^{-3}
Mass of water = Mass of object
hence, estimated mass of the elephant = V *10^{3} kgm^{-3}
c) To measure the wind speed a rotating device( anemometer) can be used. When the wind blows, wind speed is given by the number of rotations per second.
d) Area of the head surface = A
Measure the radius of the hair using the screw gauge = r
Area of the hair a = \pi r^2
The number of hair strands = \frac{\text{ Area of the head surface }}{\text{ Area of the hair }}
= \frac{A}{a} = \frac{A}{\pi r^2}
e) Calculating the number of molecules of air in the classroom
Volume of the class room V_c = lbh where, l -length, b-breadth and h - height
Volume of the air molecule(sphere in shape) V_a = \frac{4}{3} \pi r^3 where, r- radius of the air molecule
Number of molecules of air = \frac{V_a}{V_c}
= \frac{ \frac{4}{3} \pi r^3 }{lbh}
= \frac{4 \pi r^3 }{3 * lbh}
Hence, number of molecules of air in the classroom = \frac{4 \pi r^3 }{3 * lbh}