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.

Accepted Answer

D

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

Accepted Answer

D

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

Accepted Answer

The pressure of a gas is directly proportional to its temperature when the volume and the amount of gas are constant (Gay-Lussac's Law). Therefore, if the temperature increases from 300 K to 400 K, the pressure increases by the same factor: $200000 \, \text{Pa} \times \frac{400}{300} = 266667 \, \text{Pa}$.

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.

Accepted Answer

The volume of the gas in the balloon increases with temperature under constant pressure according to Charles's Law (V1/T1 = V2/T2). Given the initial volume (V1) is 5x10^16 liters at 300K, and the temperature increases to 330K, the new volume (V2) can be calculated as V2 = V1 * (T2/T1) = 5x10^16 * (330/300) = 5.5x10^16 liters.

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.

Accepted Answer

When you are moving in a circle, even if your speed is constant, your direction is constantly changing. This change in direction is a change in velocity, indicating acceleration towards the center of the circle. Static friction between you and the platform is what prevents you from sliding off; it acts towards the center of the circle (inwards), providing the centripetal force necessary for circular motion.

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

Accepted Answer

The pressure due to a column of fluid is given by $P = \rho gh$, where $\rho$ is the density of the fluid (approximately $1000 \, \text{kg/m}^3$ for water), $g$ is the acceleration due to gravity ($9.8 \, \text{m/s}^2$), and $h$ is the height of the fluid column. To double the atmospheric pressure ($100000 \, \text{Pa}$), we need an additional $100000 \, \text{Pa}$ from the water column. Solving $100000 = 1000 \times 9.8 \times h$ gives $h \approx 10 \, \text{m}$.

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.

Accepted Answer

The buoyant force on an object submerged in a fluid depends on the volume of fluid displaced by the object, not its density. Since both the plastic decoration and the rock have about the same volume and are totally submerged, they displace the same amount of water and thus experience the same buoyant force.

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.

Accepted Answer

The answer of When driving down a level smooth road,...

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.

Accepted Answer

When the air is compressed rapidly by the plunger, its temperature increases significantly due to the compression of gas, which can ignite the cotton ball. This is a demonstration of the principle that compressing a gas increases its temperature, which is related to the ideal gas law.

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.

Accepted Answer

The tiny white bubbles of steamed milk remain on the surface of the coffee because they are less dense than the coffee but more dense than the air above the coffee. This density difference allows them to float on the coffee without rising into the air.

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.

Accepted Answer

DHot air rises due to convection, which keeps it inside the balloon despite the opening at the bottom. Additionally, the propane burner heats the air, causing it to expand and rise, continually replenishing the hot air inside the balloon and preventing it from escaping through the opening.

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.

Accepted Answer

For an object to float in one liquid and sink in another, its density must be more than the density of the liquid it sinks in and less than the density of the liquid it floats in. Therefore, the object's density is between 760 kg/m^3 and 910 kg/m^3.

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.

Accepted Answer

As the balloon cools without losing or gaining air, its density increases because the air inside contracts, making it denser than the surrounding air. The buoyant force, which depends on the volume of displaced fluid (in this case, air), remains constant in terms of its calculation basis but becomes insufficient to support the balloon's increased weight due to increased density, causing it to sink.

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.

Accepted Answer

The answer of Suppose you have a car tire that...

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.

Accepted Answer

Atmospheric pressure can only support a column of water (or in this case, lemonade, which is mostly water) up to about 10 meters tall. Beyond this height, the pressure is insufficient to push the liquid upwards against gravity, which is why your friend cannot taste the lemonade from a height of 20 meters.

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.

Accepted Answer

The pressure inside a bubble is actually greater than the pressure in the surrounding water, not less. This is due to the surface tension of the bubble creating an internal pressure that is higher than the external pressure. Options A, B, and D are true and contribute to the reason why bubbles rise in 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?

Accepted Answer

The answer of It's Friday night and you decide to...

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.

Accepted Answer

Water pressure increases with depth, so the bottom of a dam experiences the highest pressure, making it more susceptible to failure if not properly designed or maintained.

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.

Accepted Answer

The principle that the speed of fluid exiting a spout increases with the height (or pressure) of the fluid in the container is based on Bernoulli's principle and the equation of continuity. The higher the fluid level, the greater the pressure at the bottom, leading to a higher exit speed.

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.

Accepted Answer

The pressure at the spout, which is related to the water level in the jug, determines the speed of the water as it exits. Higher pressure (and thus higher water level) results in higher speeds, which in turn results in the water stream landing farther from the jug. Conversely, lower pressure results in lower speeds, causing the streams to land closer to the jug.

Quiz 5: Fluids

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

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?

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?

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,

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

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.

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

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

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

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

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

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,

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.

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

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?

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