Homework 10 Problems – Properties of Fluids

Homework 10 Problems – Properties of Fluids
1. [10 points] The gravitational force exerted on a solid object is 5.00 N as measured when
the object is suspended from a spring scale as shown below. When the suspended object
is submerged in water, the scale reads 3.50 N. Find the density of the object.
2. [10 points] A boat carrying a large boulder is floating on a lake. The boulder is thrown
overboard and sinks. How should the water level in the lake (with respect to the shore)
change? Defend your answer using Archimedes’ principle.
3. [10 points] (a) Tornadoes and hurricanes often lift the roofs of houses. Explain why. Why
should you keep your windows open under these conditions? (b) Many people believe
that a vacuum created inside a vacuum cleaner causes particles of dirt to be drawn in.
Actually, the dirt is pushed in. Explain.
4. [10 points] A liquid (ρ=1.65 g/cm3) flows through a horizontal pipe of varying cross
section as seen below. In the section, the cross-sectional area is 10.0 cm2, the flow speed
is 275 cm/s, and the pressure is 1.20 x 105 Pa. In the second section, the cross-sectional
area is 2.50 cm2. Calculate the smaller section’s flow speed and pressure. (5 points)
5. [10 points] Water moves through a constricted pipe in steady, ideal flow. At the lower
point shown below, the pressure is 1.75 x 105 Pa and the pipe radius is 3.00 cm. At the
higher point located at y = 2.50 m, the pressure is 1.20 x 105 Pa and the pipe radius is
1.50 cm.
a. Find the speed of the flow in the lower section
b. Find the speed of the flow in the upper section
c. Find the volume flow rate through the pipe
Bonus: [5 points] A jet of water squirts out horizontally from a hole near the bottom of the tank,
shown below. If the hole has a diameter of 3.50 mm, what is the height h of the water level in the
tank?
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