Question

To practice tactics box 13.1 hydrostatics. in problems about liquids in hydrostatic equilibrium, you often need to find the pressure at some point in the liquid. This tactics box outlines a set of rules for thinking about such hydrostatic problems.
A) Find the pressures pa and pb at surfaces a and b in the tube, respectively. Use patmos to denote atmospheric pressure.
B) As stated in rule 3 in the tactics box, it is always convenient to use horizontal lines in hydrostatic problems. in each one of the following sketches, a different horizontal line is considered. which sketch would be more useful in solving the problem of finding the gas pressure?
C) Assume p atmos=1.00atm. What is the gas pressure pgas?

Answer 1

ANSWER:

PART A) Find the pressures pa and pb at surfaces a and b in the tube, respectively. Use patmos to denote atmospheric pressure.

Express answers, separated by a comma,in terms on one or both of the variables

            Pgas

Pa,Pb =P atmos

Part B)As stated in rule 3 in the tactics box, it is always convenient to use horizontal lines in hydrostatic problems. in each one of the following sketches, a different horizontal line is considered. which sketch would be more useful in solving the problem of finding the gas pressure?

It is useul to draw a horizontal line because it allows you to relate pressure in the mercury at crticial points in the tube. For example, even though you are not given the pressure at point c, you know that Pc=Patmos, because point C is at the same height as any point on surface B. At the same time, you can also use the hydrostatic pressure equation to relate the pressure at point C to that surfarce A, where pressure is determined by the gas pressure in the box.

Part c)Assume p atmos=1.00atm. What is the gas pressure pgas?

Conversion factor between atmospheres and pascals

1atm= 101,300 Pa

Find the height of the liquid column above point C

What is the height hc of the of the mercury column above point C?

hc= h1- h2

Pgas= Patmos - Pmg(h1 - h2) Pa