Fluid Mechanics

Pressure in a fluid: Fluid fills the container shown in the figure. At which of the indicated points is the pressure greatest?

• A

• B

• C

• D

• The pressure is the same at each of the labeled points.

Pressure in a fluid: At a certain depth in the ocean, the absolute pressure is p. If you go to twice that depth (treating the water as incompressible)

• the absolute pressure will be 2p.

• the absolute pressure will be less than 2p.

• the absolute pressure will be greater than 2p.

• the gauge pressure will not change.

• the gauge pressure will increase but will not double.

Buoyancy: Salt water is more dense than fresh water. A ship floats in both fresh water and salt water. Compared to the fresh water, the volume of salt water displaced by the ship is

• greater than the volume of fresh water.

• less than the volume of fresh water.

• the same as the volume of fresh water.

Buoyancy: A 50-cm³ block of wood is floating partially submerged in water, and a 50-cm³ block of iron is totally submerged in water. Which block has the greater buoyant force on it?

• the wood

• the iron

• Both have the same buoyant force.

• The answer cannot be determined without knowing the densities of the blocks.

Buoyancy: A rock is under water in a shallow lake. As the rock sinks deeper and deeper into water, the buoyant force on it

• increases.

• decreases

• remains constant

Buoyancy: A piece of wood is floating in a bathtub. A second piece of wood sits on top of the first piece, and does not touch the water. If the top piece is taken off and placed in the water, what happens to the water level in the tub?

• It goes up.

• It goes down.

• It does not change.

• This cannot be determined without knowing the volume of the top piece of wood.

Flow rate: Water flows through a pipe having a varying width. More water flows per second through the wide section than through the narrow section because there is more room for it to flow.

• True

• False

Bernoulli's principle: As the speed of a moving fluid increases, the pressure in the fluid

• increases.

• remains constant.

• decreases.

• may increase or decrease, depending on the density of the fluid.

Bernoulli's principle: When you blow some air above the upper face of a paper strip, the paper rises. This occurs because

• the air above the upper face of the paper moves faster, which makes the pressure higher than at the lower face.

• the air above the upper face of the paper moves faster, which makes the pressure lower than at the lower face.

• the air above the upper face of the paper moves faster but the pressure remains constant.

• the air above the upper face of the paper moves slower, which makes the pressure higher than at the lower face.

• the air above the upper face of the paper moves slower, which makes the pressure lower than at the lower face.

Bernoulli's principle: You are driving a late model convertible car at the 65 mph speed limit with its soft flexible roof closed up and the windows closed. You observe that the roof

• bows inward.

• is no different from when the car was at rest.

• bows outward.

• bows inward only when you are driving uphill.

• bows inward only when you are driving downhill.