Homework Challenge 3
Physics 212
Due 2/01/2012
1. In a pressure test chamber, a person starts acting strange when the gauge pressure exceeds 40
lb/in2. Gauge pressure is the pressure in excess of atmospheric pressure. This is a well-known
effect that limits the depth at which scuba divers should breathe pure
air. In sea water, whose density is 1.03 g/cm3, to what depth should a
diver be limited?
2. Piston 1 in the figure to the right has a diameter of 0.250 in. Piston 2 has
a diameter of 1.50 in. Determine the magnitude (F) of the force necessary to support the 500 lb. load in the absence of friction.
3. A wooden dowel (cylinder) has a diameter of 1.20 cm. It floats in water
with 0.40 cm of its diameter above water. Determine the density of the
dowel.
4. What is the smallest number of whole logs ( = 725 kg/m3, radius = 0.08 m, length =3.0 m)
that can be used to build a raft that will carry four people, each of whom has a mass of 80 kg?
5. Water is pumped from the Colorado river to Grand Canyon Village through a 15.0-cmdiameter The pipe. river is at 564 m elevation and the village is at 2096 m. (a) What is the minimum pressure the water must be pumped at to arrive at the village? (b) If 4500 m3 are pumped
per day, what is the speed of the water in the pipe? (c) What additional pressure is necessary to
deliver this flow?
6. Tests of lung capacity show that adults are able to exhale 1.5
liters of air through their mouths in as little as 1.0 seconds. (a)
If a person blows air at this rate through a drinking straw with
a diameter of 0.60 cm, what is the speed of the air in the straw?
(b) If the air from the straw in part (a) is directed horizontally
across the upper end of a second straw that is vertical, as
shown in the in figure, to what height does water rise in the
vertical straw?
7. Students in a fraternity house want to be able to spray water 25 m across their neighbors yard
onto a patio. They have a hose of inside diameter 1.2 cm that can spray a distance of only 1 m.
What size nozzle do they need?
Recitation homework problem: Chapter 15, #63