exam 2
. You are working late in the physics lab, where you measure the period of a pendulum to be 0.8 s. You fall asleep and have a dream that you are on a planet whose gravitational strength is 4 times that of the earth. If your dream is to be physically accurate, the period of the pendulum in your dream must be
0.4 s
An ideally efficient cools food to 210k. If room temperature 300k, and the machine consume 75j of work, how much heat was removed from the food?
175j 75*210/210-300
If you drop a glass vase on the floor, it will become fragments. If you drop those fragments on the floor, however, they will not become a glass vase. Why not?
A fragmented vase has higher entropy than an intact vase.
why do aluminum pains heat food much more evenly than stainless steel pans when you cook on a stove?
Aluminum has a much higher thermal conductivity than stainless steel.
Freezing and thawing cycles tend to damage road pavement during the winter, creating potholes. What provides the mechanical work that breaks up the pavement?
As the water freezes into ice and expands, it does work on the pavement.
How does pushing on the plunger of a syringe cause medicine to flow into a patient through a hollow hypodermic needle?
Bernoulli's Equation: pressure on the fluid convert to kinetic energy ( motion) of the fluid.
How would you estimate the temperature of a glowing coal in a fireplace?
By the color of the coal.
Which of the following quantities is not conserved?A: Energy B: Angular momentum C: Entropy D: Momentum
C: Entropy
Waterproof watches have a maximum depth to which they can safely be taken while swimming. Why?
Deeper the that depth the water pressure is so great it might damage the watch.
Carbon dioxide molecule is heavier than an average air particle. When it poured which way it flow
Down
Why will a rolled-up ball of aluminum foil float in water but solid aluminum will sink?
Due to the air inside, the average density of the ball is lower than water.
A diesel engine burns it fuel at a higher temperature than a gasoline engine. Why does this difference allow the diesel engine to be more efficient at converting the fuel's energy into work?
Efficiency increases when there is a larger difference between the hot and cold objects.
Why are good thermal conductors generally good electric conductors also?
Electron motions is responsible for determining both properties
Which way does an air conditioner move heat?
From a cold region to a hot region
_____________supplies part of the energy to a pendulum clock, while _____________supplies most of the energy for a balance clock.
Gravity;a spring
When someone pulls a fire alarm in a skyscraper, pumps increase the water pressure in the section of the building nearses that alarm box. how does this pressure change assist firefighter who must battle the blaze?
Greater water pressure mean the water emerges from the hoses faster, so it can spray farther.
why does the handle of a metal spoon submerged in boiling soup feel hot
Heat from the soup is transferred through the spoon by conduction.
Some fish move extremely slowly, and it's hard to tell whether they are even alive. However, if a fish is floating at a middle height in your aquarium and not at the top or bottom of the water, you can be pretty certain that it's alive. Why?
If the fish is floating at a middle height, it must be regulating its density to be equal to the density of the water, which a dead fish couldn't do.
An acquaintance claims to have built a gasoline-burning car that doesn't release any heat to its surroundings. use the second law of thermodynamics to show that this clam is impossible.
If there is no heat release, then heat in equal work out and the engine is 100% efficient, which violates the second law of thermodynamics.
Trace the transfer of energy that comes from your food.
In food that human eat there is stored chemical energy that is only released after a chemical reaction occurs in your digestive system. After the chemical reaction has occurs in your digestive system it will converted into mechanical energy for muscle movement, thermal energy for heat, and it could also be stored as a chemical energy again in a different form to be store as fatty tissue in humans.
If you operate a window air conditioner on a table in the middle of the room, the average temperature in the room will:
Increase
Boiling temperature can be increased by
Increasing pressure
A shiny, white transparent surface prevents heat transfer because:
It has emissivity of zero and reflects all light that strikes it
When you throw a hot rock into a cold puddle, what happens to the overall entropy of the system?
It increases. According to the second law of thermodynamics (the law of entropy).
If you add a little hot tea to ice water at 0 °C, the mixture will end up at 0 °C as long as some ice remains. Where does the tea's extra thermal energy go?
It melts some of the ice
If you put a warm bottle of wine in a container of ice water, the wine will cool but the ice water won't become warmer. Where is the wine's thermal energy going?
It melts some of the ice
Some air fresheners are solid materials that have strong odors. If you leave these air fresheners out, they slowly disappear. What happens to the solid material?
It sublimes into the surrounding air
your body is presently converting chemical potential energy from food in to thermal energy at a rate of about 100 J/s, or 100 W. If heat were flowing out of you at a rate of about 200 W, what would happen to your body temperature?
It would decrease.
The amplitude of her motion will gradually decrease so that she comes to a stop.
It's determined by the torsional stiffness of the chandelier's supporting cord and the chandelier's rotational mass.
How does an air conditioner cool room air?
Its evaporator absorbs heat from the room air.
Why is a harmonic oscillator a good timekeeper?
Its period is independent of its amplitude
You use your breath to inflate a large rubber tube and then ride down a snowy hill on it. After a few minutes in the snow the tube is underinflated. What happened to the air?
Its pressure decreased.
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?
Most dense first and then in order of decreasing density.
Why does a pot of water heat up and begin boiling more quickly if you cover it?
No heat is being carried away by evaporation water
Why is a car more likely to knock on a hot day than on a cold day?
On a hot day it takes less work to compress the fuel to the point where it spontaneously ignites.
what does a heat pump not do?
Perform work on its surroundings
Gravity creates
Pressure gradients in fluids
A blacksmith is forging a small piece of steel. It emerges yellow-hot ( 1000 C) from the furnace and emits more thermal radiation than your entire body. How can such a small object emit so much thermal radiation?
Radiated power is proportional to absolute temperature to the fourth power.
Even on a very humid day the hot air from your blow dryer can extract moisture from your hair. Why is heated air able to dry your hair when the air around you can't?
Relative humidity drops with rising temperature.
You're bouncing gently up and down at the end of a springboard, never leaving the board's surface. If you bounce a little farther up and down, the time it takes for each bounce will:
Remain the same.
You get a job as a dish washer to help with your college bills. The first thing the management tells you is to be very careful of the steam - it is exceedingly dangerous. In fact, steam at 100o C can burn you much more than water at 1000 C. Please explain.
Steam can burn you more than water at a higher temp because steam contains more energy due to the fact it needs a lot of it to change liquid water to vaporize.
Why doesn't heat flow naturally from cold to hot?
Such heat flow would violate the law of entropy
Putting a clear plastic sheet over a swimming pool helps keep the water warm during dry weather. Explain.
Sunlight can penetrate through to the water, and no heat is being carried away by evaporating water.
Moments before it is ignited by the spark plug, the mixture of fuel and air inside an automobile cylinder is compressed to very high density. During the compression process, the mixtures:
Temperature rises dramatically and so does its pressure.
Why aren't there any thermometers that read temperature down to -300 C
That would be lower than absolute Zero.
The outdoor portion of a central air-conditioning unit has a fan that blows air across the condenser coils. IF this fan breaks, why won't the air conditioner cool the house properly?
The air blown by the fan carries heat away from the condenser coils
Drinking fountains that actively chill the water they serve can't work without ventilation. They usually have louvers on their sides so that air can flow through them. why do they need this airflow?
The air carries heat away from the heat pump which cools the water
If you seal a soft plastic bottle or juice container while hiking high in the mountains and then return to the valley, the container will be dented inward. What causes this compression?
The air inside the container is at a lower pressure than the air outside.
Many jars have dimples in their lids that pop up when you open the jar. What holds the dimple down while the jar is sealed, and why does it pop up when the jar is opened?
The air outside is a higher pressure than the air inside the jar, which holds the dimple down. when the pressure equalizes, the dimple pops back to its normal position.
you seal a rigid container that is half full of hot food and put it in the refrigerator. why is the container's lid bowed inward when you look at it later?
The air pressure of the air outside the container pushes the lid in .
You seal a rigid container that is half full of hot food and put it in the refrigerator. Why is the container's lid bowed inward when you look at it later?
The air pressure of the air outside the container pushes the lid in.
If you place a hot, wet cup upside down on a smooth counter for a few seconds, you may find it difficult to lift up again. What is holding that cup down on the counter?
The air pressure of the air outside the cup.
It's often a good idea to wrap food in aluminum foil before baking it near the red-hot heating element of an electric oven. Why does this wrapped food cook more evenly?
The aluminum foil conducts the heat evenly to all parts of the food.
When pushing a child on a playground swing, you normally push her forward as she moves away from you. What happens if you push her forward each time she moves toward you?
The amplitude of her motion will gradually decrease so that she comes to a stop.
What keeps the air molecules in our atmosphere from piling up on the ground?
The atmosphere's thermal energy
The strongest evidence for the Big Bang theory of the origin of the universe is the thermal radiation emitted by that explosion. This radiation has cooled over the years to only 3 K and is now mostly microwaves. Why should 3K thermal radiation be microwaves?
The blackbody spectrum for a 3 K object has its peak wavelength in the microwave region of the electromagnetic spectrum.
You're floating outside the space station when your fellow astronaut tosses you a cold bottle of mineral water. It's outside your space suit but you open it anyway. It immediately begins to boil. Why?
The boling point of water is much lower at very low pressure.
You add 1 joule of thermal energy to a cold object and to a hot object. Which one experiences the greater rise in entropy (disorder)?
The cold object
A soda siphon carbonates water by injecting carbon dioxide gas into it. THe gas comes compressed in a small steel container. As the gas leaves the container and pushes its way into the water, why does the container become cold?
The gas in the container is doing work but there is no heat input.
Ice tea is often dispensed from a large jug with a faucet near the bottom. Why does the speed of tea flowing out of the faucet decrease as the jug empties?
The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.
Why is it that you can put a metal pot filled with water on a red-hot electric stove burner without fear of a damaging the pot?
The heat is conducted through the pot into the water.
A chemical rocket is a heat engine, propelled forward by its hot exhaust plume. The hotter the fire inside the chemical rocket, the more efficient the rocket can be. Explain this fact in terms of the second laws of thermodynamics.
The hotter the fuel burns , the greater the entropy increase in the system.
A doctor can study a patient's circulation by imaging the infrared light emitted by the patient's skin. Tissue with poor blood flow is relatively cool. What changes in the infrared emissions would indicate such a cool spot?
The infrared emissions from the cool spot would be less bright and shifted toward longer wavelengths.
opening a container of liquid in orbit above the earth would cause it to boil because
The lack of an atmosphere means that there is no pressure thus lowering the boiling point.
Doctors use an infrared camera to look for inflammation, which appears as a hot patch on otherwise cooler skin. What differences would the camera observe at this hot patch?
The light from the hot patch would be brighter and have a shorter wavelength than light from the surrounding skin.
Why do mats and vegetables cook much more quickly when there are metal skewers sticking through them.
The metal skewers conduct heat to the interior of the food.
When cooking a potato in a conventional oven it is useful to stick a nail in it, which make it cook faster. this is because
The nail is a good conductor of heat.
A high-flying airplane must compress the cold, rarefied outside air before delivering it ot the cabin. Why must this air be air-conditioned after the compression?
The outside air becomes hot during the compression.
If a child stands up on the seat of a playground swing, how will the swing's period be affected?
The period will decrease as the pendulum gets shorter.
A plant is a heat engine that operates on sunlight flowing from the hot sun to the cold earth. The plant is a highly ordered system with relatively low entropy. Why doesn't the plant's growth violate the second law of thermodynamics?
The plant alone is not the entire system. when you consider the plant plus all its surrounding, then there will be a net entropy increase as the plant grows.
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 fulles, net fulles, etc.) Having had a physics class, you simply open the horizontal spouts all the same height and compare where the streams land on the ground below. in terms of how far each steam lands from the jug, which of the following statements is correct.
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.
Why is atmospheric pressure lower in the mountains thanit is at sea level?
The pressure at every height in the atmosphere equal the weight of the air above it
Each time you breathe in, air accelerates toward your nose and lungs. How does the pressure in your lungs compare with that in the surrounding air as you breathe in?
The pressure in your lungs is less than that of the surrounding air.
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 following observations is not true and therefore does not help explain why the bubbles rise in your Perrier?
The pressure inside a bubble is much less than the pressure in the water around it.
If you open the door of your refrigerator with the hope of cooling your room, you will find that the room's temperature actually increases somewhat. Why doesn't the refrigerator remove heat from the room?
The refrigerator release more energy as heat than it removes from the air inside itself.
When you put a loaf of bread in a plastic bag, there is still air around the bread. Why doesn't the bread dry out as quickly in the bag as it does when there's no bag around it?
The relative humidity of the air in the bag reaches 100%.
Explain how convection contributes to the shape of a candle flame.
The rising warm air cause the flame to engate upward.
If you drop a metal rod on the floor, end first, you hear a high-pitched tone. What's happening?
The rod is vibrating as a harmonic oscillator, with its two halves first approaching one another and then moving apart.
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.
The same
You have a roll of papered foil that is shiny on one side and black on the other. You wrap a cold potato salad in that foil. Which side should be facing outward to keep the potato cold longest?
The shiny side
You have a roll of papered foil that is shiny on one side and black on the other. You wrap a hot potato in that foil. Which side should be facing outward to keep the potato hot longest?
The shiny side
on a bitter cold day, the snow is light and powdery. This snow doesn't begin melting immediately when you go into a warm room. Why?
The snow's temperature needs to rise to 0 C before it can start melting
Why are concrete sidewalks divided into individual squares rather than being left as continuous concrete strips?
The space between the squares gives the concrete room to expand on a hot day.
A child swinging on a wing set travels back and forth at a steady pace. what determines the period of the child's motion?
The strength of Earth's gravity and the length of the swing's chains.
When the gas now makes up the sun was compressed together by gravity, what happened to the temperature of that gas? Why?
The temperature rose because gravity did work on it.
A log is much heavier than a stick, yet both of them float in water. Why doesn't the log's greater weight cause it to sink?
The upward buoyant force on the log is greater than its weight.
For an object that sinks in a fluid,
The weight of fluid displaced is less than its weight.
Why must the pressure inside a whistle teakettle exceed atmospheric pressure before the whistle can begin to make noise?
The whistle is due to pressurized ( greater than atmospheric pressure) steam forcing its way out through the narrow opening.
You are a mechanic in a garage and are working on a carburetor that is made of metal, has a glass inspection window and plastic gears for the choke. If all three types of material are at the same temperature and each type of material is in contact with the other two, then
They are in thermal equilibrium
Astronomers can tell the surface temperature of a distant star without visiting it. How is this done?
They use the color temperature of the star's light.
A glass of ice water contains both ice and water. After a few minutes of settling, how do the temperatures of the ice and the water compare?
They're at the same temperature
In which direction is conduction most effective?
Through the thin wall of a metal sheet
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?
Up, equal to the can's weight
how can you reduce knocking in your car's engine?
Use higher-octane gasoline
you open the refrigerator in our room and put in a case of room- temperature root beer. aft an hour, the root beer is ice cold. IF you room air did not exchange and heat with the outdoor air during the time, the room air will be
Warmer because the refrigerator will have pumped heat out of the root beer and into the room air.
Why are failures in dams more likely to occur closer to the bottom of the dam?
Water pressure is higher at the bottom.
If you block the outlet of a hand bicycle pump and push the handle inward to compress the air inside the pump, the pump will become warmer. Why?
You are doing work on the air in the pump.
If you open the door of a freezer and stand in front of it, you'll feel cold even though no cold air is reaching you. That's primarily because:
You are radiating more heat at it than it is at you.
A metal block is attached to a spring, and undergoes harmonic oscillation horizontally. when the velocity is at its maximum to the right, the acceleration of the block is
Zero
which is more effective at heating a room:
a black woodstove
which of the following is definitely not a harmonic oscillator?
a bouncing ball
Burning something always releases thermal energy. Why doesn't burning something ever absorb thermal energy?
absorption wouldn't conserve energy
The total energy of a portion of water in steady state flow is constant
along a streamline
The reason for using a harmonic oscillator as a clock's time- keeper is so that the clock will keep accurate time even if the
amplitude of the time-keeper's oscillation changes
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
an increase in the density of the air inside the ball.
In thermal equilibrium at atmospheric pressure, ice can exist only
at or below 0 C (32 F)
As a drinking straw is made taller and taller, drinking water through it
becomes harder and eventually impossible
On a warm, balmy summer day you decide to relax by watching the latest building renovation in your neighborhood. You notice that a very heavy wrecking ball is attached to a much lighter chain and is dangling from a crane and swinging back and forth. As long as it does not swing too high the time it takes the wrecking ball to complete one full oscillation will be
both the amplitude of the motion and the weight of the ball
The _______ two temperatures are the _______ it is to move heat from hot to cold.
closer; easier
On what day a hot air balloon lift more
cold
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
convection naturally would make hot air rise, so it has no opening through which to escape.
carbon dioxide molecule is heavier than an average air particle. when it poured which way it flow
down
Gasoline with a higher octane number
has a higher ignition temperature.
In a car engine; the compression stoke involves the piston compressing the air/ gas mixture so rapidly that virtually no heat loss can occur. in the compassion stroke, the air/ gas mixture
heat because work is being done on the air/ gas mixture
The neighborhood children are playing one has lost a pocketful of change. As result they all decide to do a close inspection of the sidewalk. They notice that there are gaps in between the sidewalk filled with a felt-like material. These gaps will prevent
high stress due to thermal expansion.
If you operate a window air conditioner on a table in the middle of a room, the average temperature in the room will
increase
If you double the length of a pendulum, its period of oscillation will
increase by a factor of the square root of 2
The length of a pendulum is doubled. the period of the pendulum's oscillation
increases by a factor less than two
The length of a pendulum is doubled. The period of the pendulum's oscillation
increases by a factor less than two.
"cycles" in a four - stroke engine are
induction, compression, power, exhaust
When you drink water through a straw, the water
is pushed upward by a pressure imbalance
The amplitude of a pendulum is doubled, but remains relatively small. The period of the pendulum's oscillation
is unchanged
The amplitude of a pendulum is doubled, but remains relatively small. the period of the pendulum's oscillation
is unchanged
A diesel engine is more efficient that gasoline engine because
it has a higher temperature and can therefore convert more heat into work
The acceleration due to gravity at the moon's surface is only about one-sixth that at Earth's surface. If you took a pendulum clock to the moon, would it run fast, slow, or on time?
it would run slower
A clothing rack hangs from the ceiling of a store and swings gently back and forth. you notice that the period of the rack's oscillation doesn't depend on how many dresses the rack is holding. Insted, its period depends only on
its length and the strength of gravity
one reason for using a quartz crystal as a clock's time-keeper is so that the clock will
keep accurate time even if the ambient temperature changes.
you decide to take your younger brother to the park for fun afternoon. you notice that one ride is basically a seat attaché to an old car spring. when a person sits on it the spring vibrates rapidly but when in a car the spring vibrates much more slowly . this is because
large mass on a spring give lower frequencies
the____the temperature difference between hot and cold, the fraction of heat you can divert and transform into____.
larger;work
What does the period of a pendulum depend on?
length and gravity
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
less dense than the coffee but more dense than the air above the coffee.
A hydrogen gas particle weighs half as much as a helium gas particle. If you replace the helium in a balloon with hydrogen, it will be able to lift
less weight than it did with helium
Water seeks its level (flows until it is the same height everywhere) because that arrangement
minimize the water's total potential energy
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
moves downward slightly and floats lower in the water.
A tall flagpole is a harmonic oscillator, flexing back and forth with a steady period. the pole rises from a base that is fixed in the ground, but you can push it forward from chest height. to increase the amplitude of the pole's motion, you should push it forward when it is
moving away from you.
If you heat the top of a fluid, will natural convection carry heat to the bottom of that
no
A pedestrian bridge crosses a street. The bridge is entirely supported by columns below. A gap at each end of the bridge separates the bridge's surface from the sidewalks leading to the bridge. The width of each gap changes with time. This width is smallest:
on hot days
A pedestrian bridge crosses a street. This bridge is entirely supported by columns from below. A gap at each end of the bridges separates the bridge's surface from the sidewalks leading to the bridge. The width of each gap changes with time. This width is smallest
on hot days
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
on the ground—the lowest point on the hose.
melting is an _____ that requires energy _______ for the melting system
phase transition; input
When you pull a small tree to one side and suddenly let it go, it swings back and forth several times. you notice that the period of this motion doesn't depend on how far you bend the tree away from its normal upright position. based on the observation, you know that the restoring force that returns the tree to its upright position is
proportional to how far you bend the tree away from upright.
people fighting forest fires carry emergency tents that have shiny aluminum outer surfaces. if there is trouble a fire fighter can lie under the tent to block the heat from burning trees overhead. the tent helps because:
radiation carries heat downward toward the firefighter and the aluminum tent reflects most of that radiation
People fighting forest fires carry emergency tents that have shiny aluminum outer surfaces. If there is trouble, a fire fighter can lie under the tent to block the heat from burning trees overhead. The tent helps because
radiation carries heat downwards toward the fighter and the aluminum tens reflects most of that radiation.
You are watching a science fiction movie where people on a space ship are traveling around the universe observing stars with different temperatures. Which of the following stars has the lowest surface temperature?
reddish star
You're bouncing gently up and down at the end of a springboard, never leaving the board's surface. if you bounce a little farther up and down, the time it takes for each bounce will
remain the same
if you double the mass of a pendulum, its period of oscillation the time it taken to complete one full cycle of its motion- will
remain the same
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
shrivel up, since the atmosphere exerts more force on the can as it cools.
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
shrivel up, since the atmosphere exerts more force on the can as it cools.
you are superb proposal writer and convince Nasa to fund your taking a pendulum clock to mars studying hoi ti runs. compared to the time it should keep on earth, the clock will run.
slower
The acceleration due to gravity at the moon's surface is only about one-sixth that at the earth's surface. if you took a pendulum clock to the moon, the clock would run
slower than on earth.
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.
static variation; dynamic variation
At 100% relative humidity
steam and liquid water can coexist
Moments before it is ignited by the spark plug, the mixture of fuel and air inside an automobile cylinder is compressed to very high density. During the compression process, the mixture's
temperature rises dramatically and so does its pressure.
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,
the average density of the balloon became greater than the surrounding air and the buoyant force on the balloon became less than its weight.
which of the following clocks would keep accurate time if you took them to the moon; a pendulum clock, a balance clock and a quartz watch
the balance clock and the quartz watch
a thermoelectric cooler is type of heat pump that use electric power to move heat against its natural direction of flow. in other words, it takes energy from system and transfer it to another system which is a higher temperature. in such a heat pump transfer it to another system is at a higher temperature. in such a heat pump
the cooler requires power input because the flow a cool region to a warm region alone would decrease the entropy(disorder) of the system.
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
the density of the fish is about equal to the density of the water.
A car engine runs most efficiently when
the engine temperature is hot and it is a cold winter day.
to make it less likely that a car engine will " knock' ( have it fuel/air mixture ignite too early), the engine is designed so that
the fuel/air mixture is not compressed too tightly.
Why must tall dams be so much thicker at their bases than at their tops?
the greater the depth of the water the greater the pressure pushing on the wall of the dam
Wasp and hornet sprays proudly advertise just how far they can send insecticide. How does the pressure inside the spray can affect that distance, and why is the direction of the spray important (vertical vs. horizontal)?
the greater the pressure, the father it will spray. A vertical spray will only go up or down, so you need to spray at least a little horizontally to get any distance.
housing and natural animal fur; insulation works because
the insulating materials traps air and prevent convection
you can inflate a plastic bag by holding it up so that is catches the wind. use Bernoulli's equation to explain this effect.
the kinetic energy of the moving air converts into greater air pressure inside the bag, which inflates the bag.
When relative humidity is less than 100%
the leaving rate of water molecules exceeds the landing rate.
You fill two identical mugs with coffee, but the coffee in one mug is at a higher temperature than that in the other mug. You place the two mugs simultaneously in a microwave oven and turn it on briefly. As a result, you add 1 Joule of thermal energy to each mug. Which mug experiences the larger increase in entropy (if any)?
the mug containing the colder coffee experiences the the larger increase in entropy
when you stand in a pool with water up to your neck, you find that it's somewhat more difficult to breathe than when you're out of the water. why?
the pressure due to the depth of the water above your chest presses in on you.
The burned gas does more work on the piston during the power stroke than the piston does on the air - fuel mixture during the compression stroke because
the pressure during the power stroke is much higher than that in the compression stroke.
The efficiency of an engine is
the ratio of work done to heat input.
When driving down a level smooth road, your car tires flatten at the bottom and they nicely supports the weight of your car. HOwever when you run over a mall pointed rock the tire is punctured and fails. The rock is able to puncture the tire because
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.
Some clear toys contain two colored liquids. No matter how you tilt one of those toys, one liquid remains above the other. What keeps the upper liquid above the lower liquid?
the upper liquid is less dense than the lower liquid.
A popular classroom demonstration involves placing a paper cup with water in it on a burner, and boiling the water in the cup. Although part of the cup may burn, the part containing the water does not because
the water absorbs most of the heat from the flame.
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.
twice as big.
Ice is
unusual because it is less dense than water of the same temperature
When a fish is floating motionless below the surface of a lake, what is the amount and direction of the force the water is exerting on it?
upward, equal to the weight of the fish.
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
when the air was compressed its temperature increased.
a harmonic oscillator is an oscillator
with a restoring force proportional to its displacement from equilibrium
A harmonic oscillator is an oscillator
with a restoring force proportional to its displacement from equilibrium.
A helium balloon has mass, yet it doesn't fall to the floor.Is there a real force pushing up on the helium balloon?
yes
can liquid water be heat about it boiling temperature
yes
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,
you could bring the water up to only a certain high in the straw because the atmosphere pushes down on the surface of the water by a given amount.
