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.

part a) find the pressures pa and pb at surfaces a and b in the tube, respectively. use patmos to denote atmospheric pressure.

express your answers, separated by a comma, in terms of one or both of the variables pgas and patmos.

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?