chapter 10

An object floats in water with 3/4 of its volume submerged. What is the ratio of the density of the object to that of water?

3/4

Water flows through a 1-cm diameter pipe connected to a 1/2-cm diameter pipe. Compared to the speed of the water in the 1-cm pipe, the speed in the 1/2-cm pipe is:

4 times greater

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

8p

Two pieces of wood are on top of each other in the water. If the top piece is taken off and placed in the water, what happens to the water level in the tub? 23) A) It does not change. B) It goes up. C) It goes down. D) It cannot be determined without knowing the volumes of the two pieces of wood.

A

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? 28) A) at point A B) at point B C) It is the same at both A and B.

At point B as diameter decreases, velocity decreases, and pressure increases

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

B

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? 29) A) 2Q B) 16Q C) 4Q D) Q 2 E)

B

A boat floats in salt and fresh water, but saltwater is more dense. Where is the buoyant force greater on the boat? 18) A) in salt water B) in fresh water C) The buoyant force is the same in both cases.

C

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

C

pressure in a lake is true? (There could be more than one correct choice.) 11) A) The gauge pressure increases by ̇p. B) The absolute (total) pressure does not change. C) The absolute (total) pressure increases by ̇p. D) The gauge pressure does not change. E) The absolute (total) pressure increases, but by an amount less than ̇p.

C, D

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 ̇p, which of the following statements is correct? (There could be more than one correct choice.) 12) A) The pressure on the sides of the chamber will not increase. B) The pressure at the bottom of the oil will increase by more than ̇p. C) 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. D) The pressure at the top of the oil will increase by less than ̇p. E) The pressure everywhere in the oil will increase by ̇p.

C,E

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

D

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 = ̇V ̇t what is the flow rate in pipe A? 30) A) 8Q B) 4Q C) Q 2 D) 2Q E) 16Q

D

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 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 itA ) the wood B) Both have the same buoyant force. C) the iron D) It cannot be determined without knowing their densities. 27) When you blow some air above a paper strip, the paper rises. This

Iron Bouyant force is based on the amount of weight pushed down there is a higher mass for the same volume of iron

When a hole is made in the side of a Coke can holding water, water flows out and follows a parabolic trajectory. If the container is dropped in free fall, the water flow will:

Stop altogether. the velocity of the water in the cup becomes zero b/c it is in freefall- so no water comes out

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?

The aluminum does it is less dense, so technically easier to float than the iron

three containers are the same height and filled with the same amount of water. their base has the same SA. Which has the greatest total force on the base?

all of them are the same the base has the same SA

as shown in the figure, fluid fills the container at every point. Which has the highest pressure?

all of them have the same pressure

what pressure is responsible for you to be able to suck a liquid with a straw?

atmospheric pressure

salt water is more dense than fresh water.compared to the fresh water, the volume of water displaced in the salt water is 19) A) more. B) the same. C) less. D) Cannot be determined because we do not know the volume of the

c

When the cylinder is lowered into the water, how will the scale readings for the cylinder and the water change?

cylinder scale decreases, water's scale increases cylinder pushes down on the water bouyant force of cylinder makes it lighter

A blood platelet drifts along with the flow of blood through an artery that is partially blocked. As the platelet moves from the wide region into the narrow region, the blood pressure

decreases the speed of the platelet will increase, therefore the pressure will decrease

A helium balloon in an air-filled glass jar floats to the top. If the air is replaced with helium, what will happen to the helium balloon?

float to the bottom b/c of negative bouyancy

You put a straw into a glass of water, place your finger over the top so no air can get in or out, and then lift the straw from the liquid. You find that the straw retains some liquid. How does the air pressure P in the upper part compare to atmospheric pressure P0?

less than

You are walking out on a frozen lake and you begin to hear the ice cracking beneath you. What is your best strategy for getting off the ice safely?

make your area bigger to decrease the pressure!

does pressure of a fluid change at any given depth?

no! always the same

why does atmospheric pressure not crush us?

our cells maintain an internal pressure equal to atmospheric pressure

How is the smoke drawn up a chimney affected when there is a wind blowing outside?

smoke rises more rapidly b/c pressure is decreased at the top of the chimney

consider a brick totally immersed in water with its longest side vertical. at which side is the pressure on the brick the greatest?

the bottom of the brick

if you push a pin and a blunt pen against your face, what will determine whether your skin will be punctured?

the pressure! area of the pin is a lot smaller, so pressure will be greater

In a mercury barometer at atmospheric pressure, the height of the column of mercury in a glass tube is 760 mm. If another mercury barometer is used that has a tube of larger diameter, how high will the column of mercury be in this cas

the same

Imagine holding two identical bricks in place under water. Brick 1 is just beneath the surface of the water, while brick 2 is held about 2 feet down. The force needed to hold brick 2 in place is:

the same the amount of water that is displaced is the same, so Fb is the same

Two beakers are filled to the brim with water. A wooden block is placed in the second beaker so it floats. (Some of the water will overflow the beaker.) Both beakers are then weighed. Which scale reads a larger weight?

the weight would be the same b/c the water displaced is the same as the weight of the block

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 where it is placed, what will happen?

will stay where it was released

A person's blood pressure is generally measured on the arm, at approximately the same level as the heart. How would the results differ if the measurement were made on the person's leg instead?

would be higher bc the person's leg is lower