Deck 5: Fluids

Question 1

A popular classroom demonstration is to place a gas can on a burner and boil water in it. Left unchecked this has the potential to be a very boring demo. However the can is removed from the flame and the lid is screwed on tightly. After it cools down the can will

A) still be boring and not change.
B) shrivel up, since colder gases have less pressure.
C) bulge and expand, since colder gases are denser and exert more pressure
D) shrivel up, since the atmosphere exerts more force on the can as it cools.

Answer 1

shrivel up, since the atmosphere exerts more force on the can as it cools.

Question 2

You are bored during the summertime when school is not in session and you decide to do an experiment where you compare the properties of water and air. If the density of air is 1.25 kg/m³ and the density of water is 1000 kg/m³ , what volume of air weighs the same as 1 liter of water?

A) 0.00125 liters
B) 1.25 liters
C) 125 liters
D) 800 liters

Answer 2

800 liters

Question 3

You are a deep sea diver and are carrying out pressure tests on your air tanks, which are required by inspection rules. A gas cylinder is filled with a gas at a temperature of 300 K and pressure 200000 Pa. The temperature of the gas is then raised to 400 K. What is the new pressure?

A) 200000 Pa
B) 266667 Pa
C) 400000 Pa
D) 600000 Pa

Answer 3

266667 Pa

Question 4

You are in a hot air balloon and are hovering in the air so that the atmospheric pressure remains constant. At a temperature of 300 K your balloon holds 5x10⁶ liter of air. The sun comes out and the temperature rises to 330 K. What is the new volume of the balloon? You may assume that no air can exit or enter the balloon.

A) 5x10⁶ liter
B) 5.5x10⁶ liter
C) 4.5x10⁶ liter
D) Not enough information is given to determine.

Question 5

Imagine sitting on a merry-go-round and riding along as it spins. Assuming you are not grabbing it anywhere and are not moving with respect to the platform,

A) you are not accelerating because you aren't moving on the platform.
B) static friction (directed outwards) causes you to accelerate.
C) static friction (directed inwards) causes you to accelerate.
D) sliding friction makes you accelerate inwards.

Question 6

Atmospheric pressure is about 100000 Pa. At what depth in water does this pressure double?

A) 1 m
B) 10 m
C) 100 m
D) 1000 m

Question 7

Suppose you have an aquarium and you notice that you have a solid plastic decoration and a rock of about the same volume but twice as dense, and both are totally submerged in the water. The buoyant force on the plastic object is about ___________as that on the rock.

A) twice as big.
B) the same.
C) half as big.
D) one quarter as big.

Question 8

When driving down a level smooth road, your car tires flatten at the bottom and they nicely support the weight of your car. However when you run over a small pointed rock the tire is punctured and fails. The rock is able to puncture the tire because

A) the car has much more kinetic energy when on the rock than when on the flat road and this kinetic energy becomes potential energy in the tire.
B) when the car is on the rock almost all its weight is on the tire over the rock.
C) the car has much more gravitational potential energy when on the rock than when on the flat road and this gravitational potential energy becomes pressure potential energy in the tire.
D) the small surface area of the rock times the pressure in the tire is not enough force to support the car. Thus, the tire fails.

Question 9

In a popular classroom demonstration, a cotton ball is placed in the bottom of a strong test tube. A plunger fits inside the tube and it makes an air - tight seal. It is then pushed down very rapidly, and the cotton flashes and burns. This happens because

A) when the air was compressed its temperature increased.
B) friction between the plunger and the tube ignited the cotton.
C) cotton contains a pressure - sensitive substance that burns upon impact.
D) it's one of those demos that nobody understands.

Question 10

You stop for a cappuccino at a coffee shop and notice that the tiny white bubbles of steamed milk remain on the surface of the coffee. These air-filled bubbles stay where they are, rather than descending into the coffee or rising into the air, because they are

A) less dense than the coffee but more dense than the air above the coffee.
B) more dense than the coffee but less dense than the air above the coffee.
C) lighter than the cup of coffee but heavier than the column of air above the coffee.
D) thicker than the coffee but less thick than the air above the coffee.

Question 11

You are floating along in a hot air balloon. You look up and notice that the bottom of the balloon is open. Neglecting any diffusion of molecules, hot air remains inside the balloon despite this opening because

A) hot air has a lower pressure than cold air, so hot air is drawn into the balloon by the partial vacuum inside it.
B) hot air has more inertia than cold air and doesn't accelerate easily.
C) convection naturally would make hot air rise, so it has no opening through which to escape.
D) the propane burner located below the opening keeps pushing the hot air back into the balloon.

Question 12

Suppose you have two containers with liquid in them. One has a density of 760 kg/m³ and the other has a density of 910 kg /m³. If an object floats in one container and sinks in the other, the density of the object

A) has a value equal to the difference in densities of the two liquids.
B) must have a value equal to the average densities of the two liquids.
C) has a value less than 760 kg/m³ or greater than 910 kg/m³
D) has a value between 760 kg/m³ and 910 kg/m³.

Question 13

You are riding in a hot air balloon. You have not used the burner for some time and the balloon begins to sink. Assuming that no air is allowed to leave or enter the balloon,

A) the average density of the balloon remained constant and the buoyant force on the balloon became less than its weight.
B) the average density of the balloon became greater than the surrounding air and the buoyant force on the balloon remained constant.
C) the average density of the balloon became greater than the surrounding air and the buoyant force on the balloon became less than its weight.
D) the balloon became heavier.

Question 14

Suppose you have a car tire that is almost flat. There is a large amount of tire surface in contact with the street. When you pump the tire up there is much less tire surface contacting the road. Please explain why the change in tire pressure caused such a difference.

Question 15

Your apartment window opens 20 meters (65 feet) above a lemonade stand. Your friend lowers a long plastic tube out the window until its end enters the tank of delicious lemonade far below. She then begins to suck on the other end of the tube in hopes of getting a free drink. To her dismay, she never tastes a drop because

A) atmospheric pressure cannot support a column of lemonade 20 meters tall.
B) lemonade is too thick to pass through a tube that long.
C) the tube has an average density that is larger than that of lemonade, so the buoyant force cannot support its weight.
D) the tube's acceleration is downward, so it prevents the lemonade's velocity from being upward.

Question 16

You are seated at a table in a Paris Café, contemplating life and watching the bubbles rise upward in your glass of carbonated water. You can think of many physical reasons why those carbon dioxide bubbles should rise upward through the water. Which of the follow observations is not true and therefore does not help explain why the bubbles rise in your Perrier?

A) A bubble displaces more than its weight of water.
B) The pressure below a bubble is greater than the pressure above it.
C) The pressure inside a bubble is much less than the pressure in the water around it.
D) A bubble's average density is less than that of water.

Question 17

It's Friday night and you decide to take part in one of life's finest pleasures - going out to eat. The waiter is your lab partner in physics class so you play a trick on him. You place his tip in an upside down glass about ¾ full of water, which is affixed to the smooth table surface. Why does the water stay in the glass?

Question 18

Why are failures in dams more likely to occur closer to the bottom of the dam?

A) Water is considerably more dense at the bottom.
B) Water pressure is higher at the bottom.
C) The temperature is higher at the bottom.
D) Water weighs more at the bottom.

Question 19

You work with a catering firm and have been given a challenge. By emptying several liquid beverage dispensers, you have to rank them in order of their content (which one is fullest, next fullest, etc.) Having had a physics class, you devise a scheme to compare the speeds of the fluids exiting the spouts at the bottom of the containers. The principle you base your prediction on is:

A) the pressure (and hence water level) is lower when the speed is lower.
B) the volume is lower so the speed is lower.
C) what were you thinking!? The speeds won't depend upon fluid level
D) the speed increases when there is more air in the jug.

Question 20

You work with a catering firm and have been given a challenge. By emptying several liquid beverage dispensers, you have to rank them in order of their content (which one is fullest, next fullest, etc.) Having had a physics class, you simply open the horizontal spouts all from the same height and compare where the streams land on the ground below. In terms of how far each stream lands from the jug, which of the following statements is correct:

A) The pressure (and hence water level) is lower when the speed is lower. Lower speeds result in smaller ranges and the streams will land closer to the jug.
B) The pressure (and hence water level) is higher when the speed is lower. Lower speeds result in smaller ranges and the streams will land closer to the jug.
C) The pressure (and hence water level) is lower when the speed is lower. Lower speeds result in larger ranges and the streams will land closer to the jug.
D) Water speed has no effect on pressure.

Question 21

You are camping in the breathtaking mountains if Colorado. You spy an unopened diet soda can floating motionless below the surface of a lake. What is the direction and amount of force the water exerts on it?

A) Zero
B) Down, equal to the can's weight
C) Up, equal to the can's weight
D) Not enough information is given

Question 22

Lead sinkers actually float on the surface of liquid mercury. Which takes up more space: 1 kg of mercury or 1 kg of lead?

A) Mercury
B) Lead
C) Neither take up any space
D) Not enough information is given

Question 23

A popular drink is composed by pouring several types of beverage (one on top of the other) in order to get a layering effect. In what order should the individual beverages be poured into the glass so that your drink is stable?

A) Least dense first and then in order of increasing density.
B) Most dense first and then in order of decreasing density.
C) Most dense on the top and bottom to hold the least dense fluids in the middle.
D) Not enough information is given

Question 24

Water weighs about 10 N per liter. A 4.0 liter ball is pushed underwater. What is the buoyant force on the ball?

A) 4.0 liters
B) 10 N
C) 20 N
D) 40 N

Question 25

Water weighs about 10 N per liter. A 4.0 kg ball floats on the water's surface. What is the weight of the water being displaced by the ball?

A) Much less than 2000 N
B) Much more than 40 N
C) About 40 N
D) Not enough information is given

Question 26

Why will a rolled - up ball of aluminum foil float in water but solid aluminum will float?

A) It won't - the ball will sink.
B) Due to the air inside, the average density of the ball is lower than water.
C) Aluminum is less dense than water anyway.
D) Water cannot get in to equalize the pressure.

Question 27

One warm spring day you and some friends go to the beach at a nearby lake. You are tossing a soft, almost fully inflated beach ball around when someone accidentally knocks it into the lake. Although it is a warm day, the water is still very cold so nobody wants to retrieve the ball. You notice that the ball seems to have deflated somewhat after sitting in the water for a while. The contact with the cool water has caused the temperature of the air inside the ball to drop, resulting in

A) a decrease in the pressure inside the ball.
B) an increase in the density of the air inside the ball.
C) a decrease in the density of the air inside the ball.
D) an increase in the pressure inside the ball.

Question 28

You are trying to deliver water to a sink in the tree house in your backyard. You run an old hose from the spigot behind your home, across your yard, and up the tree to a sink inside the tree house. You let water fill the hose all the way to the tree house sink and then leave the hose pressurized overnight, with no water flowing in it. Unfortunately, the hose cannot tolerate high pressure anymore and it springs a leak around midnight. By morning your whole backyard is a swamp. The most likely site for the leak is

A) on the way up the tree-the most vertical portion of the hose.
B) on the ground-the lowest point on the hose.
C) at the spigot-the first point on the hose.
D) at the sink-the highest point on the hose.

Question 29

The brake system in most cars makes use of a hydraulic system. This system consists of a fluid filled tube connected at each end to a piston. Assume that the piston attached to the brake pedal has a cross sectional area of one half a square inch and the piston attached to the brake pad has a cross section area of two square inches. When you apply a force of 10 pounds to the piston attached to the brake pedal, the force at the brake pad will be,

A) 5 pounds.
B) 10 pounds.
C) 20 pounds.
D) 40 pounds.

Question 30

The Coelocanth is a very interesting, quite primitive fish that live deep in the ocean. Watching these beautiful creatures on a nature documentary, you notice that they are able to stay basically at one position in the water with only slight movements of its lobed fins. This indicates that

A) you don't have to be athletic to get on a documentary.
B) the density of the fish is less than the density of the water.
C) the density of the fish is greater than the density of the water.
D) the density of the fish is about equal to the density of the water.

Question 31

A block of hardwood is floating easily on the surface of a lake. As a storm approaches, the density and pressure of the air above the lake begin to decrease. As a result of this decrease in air pressure and density, the block of wood

A) moves upward slightly and floats higher in the water.
B) continues to float just as it did before.
C) moves downward slightly and floats lower in the water.
D) sinks to the bottom of the lake.

Question 32

As we have studied, columns of water and those of air are fundamentally important in earth science. Using three similarities and three differences please compare and contrast columns of water and columns of air.

Question 33

For an object that is floating on a fluid,

A) The weight of fluid displaced is less than its weight.
B) The weight of the fluid displaced is greater than the object's weight.
C) The weight of the fluid displaced equals the object's weight.
D The weight of the object becomes less than in air.

Question 34

For an object that sinks in a fluid,

A) The weight of fluid displaced is less than its weight.
B) The weight of the fluid displaced is greater than the object's weight.
C) The weight of the fluid displaced equals the object's weight.
D) The weight of the object becomes more than in air.

Question 35

For an object that is neutrally buoyant in a fluid,

A) The weight of fluid displaced is less than its weight.
B) The weight of the fluid displaced is greater than the object's weight.
C) The weight of the fluid displaced equals the object's weight.
D) The object has zero weight.

Question 36

Suppose you have an aquarium and you notice that you have a solid plastic decoration and a rock of about the same mass but the decoration is twice as large as the rock. Both are totally submerged in the water. The buoyant force on the plastic object is about ___________as that on the rock.

A) twice as big.
B) the same.
C) half as big.
D) one quarter as big.

Question 37

Water weighs about 10 N per liter on Earth. A 4.0 liter ball is pushed underwater on the space shuttle, where gravity was 1/10 that on Earth. What is the buoyant force on the ball?

A) 1N
B) 10 N
C) 4 N
D) 40 N

Question 38

For your high school science project you are able to get community support and terraform Mars, so that liquid water could exist on its surface. Suppose you have two cans of soda - one barely floats and one barely sinks in fresh water on Earth. Taking them to Mars, with the gravitational acceleration being 1/3 its value on earth,

A) Both objects will now float because they are lighter.
B) The buoyant behavior of the two objects will be the same.
C) Both objects will sink because the water is lighter.
D) We can't say anything until we know if the water on Mars is freshwater or not.

Question 39

Suppose you are ill and have to go to the hospital for shot. When the nurse points the fluid - filled syringe skyward to clear the air out of it, he presses the plunger down but no fluid comes out because the needle is plugged. When the plunger is pressed down and no fluid is moving,

A) The pressure of the fluid in the needed is much less than in the larger syringe.
B) The pressure of the fluid in the needle is much more than in the larger syringe.
C) The pressure of the fluid in the needle and much larger syringe are the same.
D) The pressure of the fluid everywhere is zero.

Question 40

You and your family are on a trip to the local museum and you notice that in the aquarium there are four fish: fish 1 is floating, fish 2 is stationary 2m below the water's surface, fish 3 is stationary 4 m below the water's surface and fish 5 is on the sand at bottom of the tank. (Note: things don't look good for fish 1 and fish 4 but that's beside the3 point here) Your Mom says that she'll buy you lunch if you rank the densities of the fish in order of increasing density, including the density of water in your ranking. Please select your ranking below.

A) 1B) 1<2=3=water<4
C) 4<3<2D) 4<3=2=water<1

Question 41

Suppose you throw a party to recognize that your physics class is over for the semester. You are out at a local pub with your friends and you make the comment "Look at that quarter sitting at the bottom of the aquarium. I now can tell you that its apparent weight is zero because it is underwater and supported by a buoyant force equal to the weight of the water it displaces". If your instructor were along and correctly commented on the scientific accuracy of your comment, what would they say?

Question 42

Gravity creates

A) Constant motion in fluids
B) Lack of pressure on the top of all fluids
C) Uniform pressure in fluids
D) Pressure gradients in fluids

Question 43

The pressure gradient set up in water standing is a glass is an example of ________ ________ in pressure, while variations in pressure due to water flowing faster in the smaller parts of a pipe are a type of ________ ________ in pressure.

A) static variation; buoyant force
B) static variation; dynamic variation
C) dynamic variation; constant value
D) dynamic variation; dynamic constancy

Question 44

Suppose you had a very long straw that could reach from a cup of water on the ground level to the top of a very tall building. When you suck on the straw in order to bring water up,

A) You could drink the water at any height with no problem
B) You could bring the water up to only a certain height in the straw because the atmosphere pushes down on the surface of the water by a given amount.
C) You could bring the water up to only a certain height in the straw because after it will flash freeze in the cup.
D) Water is too thick to be pulled up in the straw by more than a few inches.

Question 45

Cities have to use water towers to supply water to because

A) The water tower has a vault of air that is pressurized.
B) Water moves fastest at the bottom of the water tower and this speed is transmitted uniformly throughout all water pipes below.
C) Water pressure at the top of the tower is transmitted through the water pipes.
D) Water pressure at the bottom of the tower is much higher than at the top.

Question 46

If the water pressure at a pump station at sea level 4,000,000 Pa, how high can the water be pumped uphill, and how fast will it flow out of a faucet at a washing station at sea level?

A) 408m; 90 m/s
B) 102m; 45 m/s
C) 102m; 90 m/s
D) 408 m; 45 m/s

Question 47

Pressure potential energy

A) Can be stored for long periods of time to be transported and used.
B) Has to do with describing moving water and is only an abstract concept.
C) Has units of pressure.
D) Exists only in stationary fluids.