Anyone good in physics? please do help me!! i need the answer a.s.a.p!?

Question

the pressure of air at the base of a tall building was found 2 b 75.5 cmHg while d pressure at d top of d building was 72.0 cmHg.

Calculate:

i) d pressure of d air at d base & d top of d building in units of Pa.

ii) d height of d building

(density of mercury = 13.6x10kgm, density of air near d earth's surface = 1.36kgm-3(superscript), g=10ms-2(superscript)..

Answer 1

1.  There must be a units conversion factor for converting cm Hg to Pa or atmospheres.

2.  There must be a function whereby % delta (pressure) = k(% delta(altitude) and k is a proportionality constant.  Plug in the pressure values and calculate the height of the building.

Answer 2

I think your figure for the density of mercury should be 13.6 * 10^3 kg/m^3.

The pressure (P) at the bottom of a column of liquid is just:

P = rho * g * h

where rho is the density of the liquid and h is the height of the column.

At the base of the building, P = 13.6 * 10^3 * 10 * 0.755 = 102680 Pa

[Note that the height needs to be in meters, not cm!]

At the top of the building P = 13.6 * 10^3 * 10 * 0.72 = 97920 Pa

The column of air equal to the height of the building therefore contributes a pressure of 102680 - 97920 = 4760 Pa

So just work the problem again for the air column:

4760 = 1.36 * 10 * h

h = 350 m

Answer 3

You have written density of mercury = 13.6x10kgm.

I think you mean 13.6x10^3 kgm-3

Finding coversion between cm Hg and Pa: -

1 meter Hg pressure = density of mercury * g * 1 meter

= 13.6 * 10^3 * 10 * 1 Pa

= 1.36 * 10^5 Pa

Therefore, 1 cm Hg = 1.36 * 10^5 * 10^-2 Pa = 1.36 * 10^3 Pa (because 1 cm = 10^-2 m)

a) Pressure at the base = 75.5 cm = 75.5 * 1.36 * 10^3 Pa

= 1.03 * 10^5 Pa

Pressure at the top = 72.0 cm = 72.0 * 1.36 * 10^3 Pa

= 0.98 * 10^5 Pa

ii) Pressure of air decreases with height by dgh

where d = density of air, h = height

Therefore, h = difference in pressure/(dg)

= (75.5 * 1.36 * 10^3 - 72.0 * 1.36 * 10^3)/(1.36 * 10) m

= 1.36 * 10^3 * (75.5 - 72.0)/(1.36 * 10) m

= 10^2 * (75.5 - 72.0) m

= 350 m

Ans: 350 m