An inverted tube, sealed at the top, holds a 20 cm column of mercury. What is the air pressure at the top of the tube? Atmospheric pressure is 76 cm Hg. Art .. Give the answer in cm RT. Art., in the form of a number without titles.
To calculate the pressure value in the upper part of the tube under consideration, we project the forces onto the vertical axis: Ftm = Fv + Ft; Rathm * S = Pv * S + Pрт * S; Ratm = Pv + Prt, whence we express: Pv = Ratm – Prt.
Constants and variables: Rathm – atmospheric pressure (according to the condition Rathm = 76 cm Hg); Pрт – pressure of a column of mercury (Pрт = 20 cm Hg. Art.).
Calculation: Pw = Ratm – Pрt = 76 – 20 = 56 cm Hg. Art.
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