$2\mathrm{.}11$ Pressure and Hydrostatic Head

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$3.$ An evaporator shows a reading of $40$kPa vacuum. What is the absolute pressure in the evaporator in kilopascals?

$4.$ A U$-$tube manometer filled with mercury is connected between two points in a pipeline. If the manometer reading is $26mmHg,$ calculate the pressure difference in kilopascals between the points when $($a$)$ water is flowing through the pipeline, and $($b$)$ air at atmospheric pressure and $20C$ with a density of $1\mathrm{.}20k\frac{g}{m^3}$ is flowing in the pipeline.

Thought Problems

When you lie motionless on a bed, the bed supports you with a force that exactly matches your weight, and when you do the same on the floor, the floor pushes up against you with the same amount of force. Why does the bed feel softer than the floor?

$2$ fyou push the tube down into the water as shown in Figure SAT$2\mathrm{.}11$TP$2$ so that