Unit 8 check

Unit 8 check: Fluids

10 questions from 4 lessons in Unit 8. Answer each one, and if you miss, follow the link back to where it is taught, then try again. Your score counts first tries.

Question 1 · from 8.1 · Sort it

Each card describes a substance's particles or how the substance behaves. Tap a card, then the state of matter it describes.

Solid

Liquid

Gas

Question 2 · from 8.2 · Fill the statement

A sealed plastic syringe is completely full of water, which you treat as incompressible, and you push hard on its plunger. Tap a blank, then a phrase.

The water presses on the plunger because huge numbers of water particles it every second. Pushing harder raises the water's pressure, but its volume . The water presses on the plunger, the barrel's wall and the sealed tip alike, each time with a force to that surface.

Question 3 · from 8.3 · Calculate

A stone with a volume of $4.0 \times 10^{- 4} m^{3}$ and a mass of 1.2 kg hangs at rest from a thread, completely under the surface of a tank of seawater and clear of the bottom. Seawater has a density of 1030 kg/m³. How large is the buoyant force the seawater exerts on the stone? Give your answer to the nearest 0.01 N.

Your answer N

Setup for question 4

A new situation, with Torricelli's theorem and the volume flow rate working together. A rainwater tank collects water off a roof, and a spigot near its bottom fills a watering can. The tank is wide, so while one can fills, its water level drops by only a few centimeters, small next to its depth.

Question 4 · from 8.4 · Calculate

The water surface in a wide, open rainwater tank is 1.25 m above the opening of a spigot near its bottom. The spigot is open to the air, and its opening has a cross-sectional area of $1.5 \times 10^{- 4} m^{2}$ . Treat the water as an ideal fluid and its level as staying put while a 9.0 L watering can fills, where $1 L = 1.0 \times 10^{- 3} m^{3}$ . How long does the can take to fill? Give your answer to the nearest 0.1 s.

Your answer s

Question 5 · from 8.1 · Decide and justify

In 1927 a physicist heated some pitch, a black, tar-like material, poured it into a glass funnel and let it cool. Three years later he cut open the funnel's stem. Cold pitch feels hard, and a sharp hammer blow shatters it. Yet ever since, the cold pitch has been creeping out through the stem, and a new drop falls about once a decade. Is pitch a fluid?

Which reason supports your answer?

Question 6 · from 8.2 · Match

A pond holds fresh water, density 1000 kg/m³, under air at 100 kPa. Tap a pressure in the pond, then its value.

Question 7 · from 8.3 · Decide and justify

A steel cargo ship floats at rest in a calm harbor, even though steel is about eight times as dense as seawater. A visitor says the seawater must push up on the ship harder than gravity pulls it down, or the ship would sink. Is the visitor right?

Which reason supports your answer?

Setup for question 8

Water flows steadily through a farm's irrigation line, passing through section A, then section B, then section C. The water is an ideal fluid of density $1000 {kg/m}^{3}$ and fills the line. Sections A and B are at the same height, and section C is on a rise. In section A the water moves at 1.50 m/s.

The irrigation line's sections
Section	Cross-sectional area (m²)	Height above section A (m)
A	0.0120	0.0
B	0.0060	0.0
C	0.0120	4.0

Question 8 · from 8.4 · Calculate

Using the irrigation line's table, with the water moving at 1.50 m/s in section A: what is the volume flow rate through section B, in liters per second? One liter is $1.0 \times 10^{- 3} m^{3}$ . Give your answer to the nearest 1 L/s.

Your answer L/s

Question 9 · from 8.1 · Calculate

A solid metal block measures 4.0 cm by 5.0 cm by 10.0 cm and has a mass of 540 g. What is the density of the metal, in kg/m³? Give your answer to the nearest 10 kg/m³.

Your answer kg/m^3

Setup for question 10

Now the fluid is air, and it is holding something up. A cylinder stands upright with its bottom sealed, and a piston rests on the air trapped inside it, held up by nothing else. The outside air presses down on the piston's top face, and the trapped air presses up on its bottom face. Each of those pushes is a pressure times an area, perpendicular to the face.

Question 10 · from 8.2 · Draw the forces

A piston, a light disk with a lead weight fixed to its top, 10 kg in all, rests on air trapped in an upright cylinder whose bottom is sealed. Treat the disk and the weight as one object, the piston. Each face of the disk has an area of 0.0020 m², friction between the piston and the cylinder wall is negligible, and the outside air, at $1.0 \times 10^{5}$ Pa, presses on the piston's top face. Build the free-body diagram of the piston, and set each arrow's length to compare the forces.

The dot is the piston.

Pick each force exerted on the piston, then choose the way it points and how long its arrow is compared with the others. The arrows are drawn for you.

0 of 10 answered.