Physics CH 10

When a box rests on a round sheet of wood on the ground, it exerts an average pressure p on the wood. If the wood is replaced by a sheet that has half the diameter of the original piece, what is the new average pressure?

4 ρ

A styrofoam sphere of radius R has a density ρ. You now carefully compress the sphere so its radius is R/2. What is the density of the compressed sphere?

8 ρ

When a heavy metal block is supported by a cylindrical vertical post of radius R, it exerts a force F on the post. If the diameter of the post is increased to 2R, what force does the block now exert on the post?

F

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 does not change

A piece of iron rests on top of a piece of wood floating in a bathtub. If the iron is removed from the wood, and kept out of the water, what happens to the water level in the tub?

It goes down

The water pressure to an apartment is increased by the water company. The water enters the apartment through an entrance valve at the front of the apartment. Where will the increase in the static water pressure be greatest when no water is flowing in the system?

It will be the same at all faucets

As a rock sinks deeper and deeper into water of constant density, what happens to the buoyant force on it if it started above the surface of the water?

The buoyant force first increases and then remains constant.

Salt water has greater density than fresh water. A boat floats in both fresh water and in salt water. Where is the buoyant force greater on the boat?

The buoyant force is the same in both cases.

If atmospheric pressure increases by an amount Δp, which of the following statements about the pressure in a lake is true? (There could be more than one correct choice.)

The gauge pressure does not change. & The absolute (total) pressure increases by Δp.

A closed cubical chamber resting on the floor contains oil and a piston. If you push down on the piston hard enough to increase the pressure just below the piston by an amount Δp, which of the following statements is correct? (There could be more than one correct choice.)

The increase in the force on the top of the chamber will be the same as the increase in the force on the bottom of the chamber. & The pressure everywhere in the oil will increase by Δp.

A spherical ball of lead (density 11.3 g/cm3) is placed in a tub of mercury (density 13.6 g/cm3). Which answer best describes the result?

The lead ball will float with about 17% of its volume above the surface of the mercury.

As shown in the figure, fluid fills a container having several sections. At which of the indicated points is the pressure greatest?

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

A boat loaded with rocks is floating in a swimming pool. If the rocks are thrown into the pool, the water level in the pool, after the rocks have settled to the bottom,

falls

A steel ball sinks in water but floats in a pool of mercury, which is much denser than water. Where is the buoyant force on the ball greater?

floating on the mercury

Consider a brick that is totally immersed in water, with the long edge of the brick vertical. The pressure on the brick is

greatest on the bottom of the brick.

An air bubble underwater has the same pressure as that of the surrounding water. As the air bubble rises toward the surface (and its temperature remains constant), the volume of the air bubble

increases

Salt water is denser than fresh water. A ship floats in both fresh water and salt water. Compared to the fresh water, the volume of water displaced in the salt water is

less

A wooden block contains some nails so that its density is exactly equal to that of water. If it is placed in a tank of water and released from rest when it is completely submerged, it will

remain where it is released.

When you blow some air above a paper strip, the paper rises. This happens because

the air above the paper moves faster and the pressure is lower

A 10-kg piece of aluminum sits at the bottom of a lake, right next to a 10-kg piece of lead, which is much denser than aluminum. Which one has the greater buoyant force on it?

the aluminum

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

the iron

A waiter fills your water glass with ice water (containing many ice cubes) such that the liquid water is perfectly level with the rim of the glass. As the ice melts

the liquid-water level decreases.

A hollow sphere of negligible mass and radius R is completely filled with a liquid so that its density is ρ. You now enlarge the sphere so its radius is 2R and completely fill it with the same liquid. What is the density of the enlarged sphere?

ρ