Reading of a barometer at the top and ground floors of a buliding are 75.000 cm. and 75.125 cm. respectively. The density of mercry is ` 13600 kg//m^2` and that of air is `1.36 kg//m^2` What is the height of the buliding ?

Answer

12.5 m

Explanation

Pressure difference ` = 75.125 - 75.000 xx 10^(-2) xx 13600 xx 9.8`
` = 0.125 xx 10^(-2) xx 13600 xx 9.8 Pa` if h is the height of the building, this pressure differecen must be equal to the pressure due to a column of air of height h, i.e., ` h rho f = 0.125 xx 10^(-2) xx 13600 xx 9.8`
or `h = (0.125 xx 10^(-2) x 13600 xx9.8)/(1.36xx9.8) = 12.5m`