Conceptual Questions (Ch. 10)

Two horizontal pipes have the same diameter, but pipe B is twice as long as pipe A. Water undergoes viscous flow in both pipes, subject to the same pressure difference across the lengths of the pipes. If the flow rate in pipe B is Q = what is the flow rate in pipe A? Q=deltaV/deltat A) 2Q B) 4Q C) 8Q D) 16Q E) Qsqrt2

A) 2Q

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? A) 4p B) 2p C) p D) p/2 E) p/4

A) 4p

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.) A) The pressure everywhere in the oil will increase by Δp. B) The pressure at the bottom of the oil will increase by more than Δp. C) The pressure at the top of the oil will increase by less than Δp. D) The pressure on the sides of the chamber will not increase. E) 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.

A) The pressure everywhere in the oil will increase by Δp. E) 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.

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? A) floating on the mercury B) submerged in the water C) It is the same in both cases. D) It cannot be determined from the information given.

A) floating on the mercury

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 A) increases. B) decreases. C) remains constant. D) increases or decreases, depending on the rate it rises.

A) increases.

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? A) the aluminum B) the lead C) Both have the same buoyant force. D) It cannot be determined without knowing their volumes

A) the aluminum

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, A) the liquid-water level remains flush with the rim of the glass. B) the liquid water level rises, causing water to run down the outside of the glass. C) the liquid-water level decreases.

A) the liquid-water level remains flush with the rim of the glass.

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? A) It goes up. B) It goes down. C) It does not change. D) It is impossible to determine from the information given.

B) It goes down.

Substance A has a density of 3 g/cm3 and substance B has a density of 4 g/cm3. In order to obtain equal masses of these two substances, what must be the ratio of the volume of A to the volume of B?

B) VA/VB = 4/3

Water flows through a pipe. The diameter of the pipe at point B is larger than at point A. Where is the water pressure greatest? A) at point A B) at point B C) It is the same at both A and B

B) at point B

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, A) rises. B) falls. C) stays the same.

B) falls.

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 water displaced in the salt water is A) more. B) less. C) the same. D) Cannot be determined because we do not know the volume of the ship.

B) less.

When you blow some air above a paper strip, the paper rises. This happens because A) the air above the paper moves faster and the pressure is higher. B) the air above the paper moves faster and the pressure is lower. C) the air above the paper moves faster and the pressure remains constant. D) the air above the paper moves slower and the pressure is higher. E) the air above the paper moves slower and the pressure is lower.

B) the air above the paper moves faster and the pressure is lower.

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? A) the wood B) the iron C) Both have the same buoyant force. D) It cannot be determined without knowing their densities.

B) the iron

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? A) It goes up. B) It goes down. C) It does not change. D) It cannot be determined without knowing the volumes of the two pieces of wood

C) It does not change.

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? A) at a faucet close to the entrance valve B) at a faucet far from the entrance valve C) It will be the same at all faucets. D) There will be no increase in the pressure at the faucets.

C) It will be the same at all faucets.

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.) A) The absolute (total) pressure does not change. B) The absolute (total) pressure increases, but by an amount less than Δp. C) The absolute (total) pressure increases by Δp. D) The gauge pressure increases by Δp. E) The gauge pressure does not change.

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

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? A) The buoyant force keeps increasing steadily. B) The buoyant force remains constant. C) The buoyant force first increases and then remains constant. D) The buoyant force steadily decreases.

C) 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? A) in salt water B) in fresh water C) The buoyant force is the same in both cases.

C) The buoyant force is the same in both cases.

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? A) The lead ball will float with about 83% of its volume above the surface of the mercury. B) The lead ball will float with its top exactly even with the surface of the mercury. C) The lead ball will float with about 17% of its volume above the surface of the mercury. D) The lead will sink to the bottom of the mercury.

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

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 A) rise to the surface. B) sink to the bottom. C) remain where it is released

C) remain where it is released.

Two horizontal pipes are the same length, but pipe B has twice the diameter of pipe A. Water undergoes viscous flow in both pipes, subject to the same pressure difference across the lengths of the pipes. If the flow rate in pipe A is Q = , what is the flow rate in pipe B? A) 2Q B) 4Q C) 8Q D) 16Q E) Qsqrt2

D) 16Q

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? A) F/4 B) F/2 C) F/sqrt2 D) F E) 2F

D) F

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? A) 8 ρ B) 4 ρ C) ρ/2 D) ρ E) ρ/8

D) ρ

3) 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? A) 2 ρ B) 4 ρ C) ρ D) ρ E) 8 ρ

E) 8 ρ

As shown in the figure, fluid fills a container having several sections. At which of the indicated points is the pressure greatest? A) A B) B C) C D) D E) The pressure is the same at each of the labeled points

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

Consider a brick that is totally immersed in water, with the long edge of the brick vertical. The pressure on the brick is A) the same on all surfaces of the brick. B) greatest on the face with largest area. C) greatest on the top of the brick. D) greatest on the sides of the brick. E) greatest on the bottom of the brick.

E) greatest on the bottom of the brick

A cubical block of stone is lowered at a steady rate into the ocean by a crane, always keeping the top and bottom faces horizontal. Which one of the following graphs best describes the absolute (total) pressure p on the bottom of this block as a function of time t if the block just enters the water at time t = 0 s?

increases linearly from a pressure higher than 0 on graph

A cubical block of stone is lowered at a steady rate into the ocean by a crane, always keeping the top and bottom faces horizontal. Which one of the following graphs best describes the gauge pressure p on the bottom of this block as a function of time t if the block just enters the water at time t = 0 s?

increases linearly from origin

A cubical block of stone is lowered at a steady rate into the ocean by a crane, always keeping the top and bottom faces horizontal. Which one of the following graphs best describes the buoyant force B on this block as a function of time t if the block just enters the water at time t = 0 s?

increases linearly from the origin on the graph then levels off