# What is the fractional decrease in pressure when a...

What is the fractional decrease in pressure when a barometer is raised 35 m to the top of a building? (Assume that the density of air is constant over that distance.)

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What is the fractional decrease in pressure when a barometer is raised 35 m to the top of a building? (Assume that the density of air is constant over that distance.)

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## Answers ( 4 )

change in pressure , ?P = ?gh

where,

? = density of medium = 1.184 kg/m

^{3}(for airat 25^{0}C)g = acc due to gravity = 9.8 m/s

^{2}h = height change = 35 m

=> ?P = 1.184*9.8*35 = 406.112Pa

1 atm = 101325 Pa

=> 1 Pa = 1/101325 atm

=> 406.112 Pa = 406.112/101325 = 0.004atm (approx)

The variation of Pressure with allitude is given by theequationP = P_{o}e^{- ( ?og /Po)h}The constant ( ?_{o}g / P_{o}) = (1.29kg/m^{3}*9.8m/s^{2}) / ( 1.013*10^{5}N/ m^{2})= 1.25*10^{-4}/ mTherefore, P = 1.004*10^{5}N/m^{2}The fractional decrease P -P_{o}= 442N/m^{2}^{3}(temperaturerange from -25 to +35 deg C) http://en.wikipedia.org/wiki/Density .^{3}*9.8*35 = 389.4*10^{-5}Pa