Physics final
Which system is in a state of stable equilibrium?
A marble in the bottom of a spherical bowl.
When someone pulls a fire alarm in a skyscraper, pumps increase the water pressure in the section of the building nearest that alarm box. How does this pressure change assist firefighters who must battle the blaze?
Greater water pressure means the water emerges from the hoses faster, so it can spray farther.
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.
Consider a 100 kg Father and his 20 kg girl. They decide to enjoy balancing on a seesaw, which is a uniform board 4 m long and pivoted exactly at its center. If girl sits at the seesaw's end (2m from the center), how far from the center on the other side should the father sit?
0.4 m
The density of gold is 19 times that of water. If you take a gold crown weighing 30 N and submerge it in water, what will the buoyant force on the crown be?
1.6 N
How much force is the air exerting on the front surface of the book with dimensions 18 x 27 cm? Assume atmospheric pressure equal to 100,000 Pa.
4860 N
The earth exerts a downward force of 850 N on a veteran astronaut as he works outside the space shuttle. What force (if any) does the astronaut exert on the earth?
850 N upward
Which of the following is definitely not a harmonic oscillator?
A bouncing ball
Burning something always release thermal energy. Why doesn't burning something ever absorb thermal energy?
Absorption is statistically unlikely
You are holding two balls that are the same size, but one is much heavier than the other. You roll them across the floor toward a ramp. The surface of that ramp is flat and rising, so the balls start moving uphill on it. While the two balls are on the surface of that ramp, what must be true of their motions? (neglect air and friction effects)
Both balls will accelerate downhill along the ramp's surface.
When your car goes out of control on an icy road, it is safest to use either the clutch or gear shift to allow your car to coast and not be powered by the engine. Why is this so?
Coasting allows the wheels to rotate so as to recover static friction again.
To modify the pitch of a guitar string you could change its mass, its tension, or its length. To raise its pitch by changing one of those characteristics at a time, how should you change those characteristics?
Either reduce the string's mass, increase its tension, or decrease its length.
Which way does an air conditioner move heat?
From a cold region to a hot region
An elastic ball that wastes 30% of the collision energy as heat when it bounces on a hard floor will rebound to 70% of the height from which it was dropped. Explain the 30% loss in height.
Gravitational potential energy is proportional to height.
Neglect air resistance in this question. If you drop a ball from a height of 4.9 m, it will hit the ground 1 s later. If you fire a bullet exactly horizontally from a height of 4.9 m, it will also hit the ground 1 s later. Explain.
Gravity acts only in the vertical direction.
A RIF (reduced injury factor) baseball has the same coefficient of restitution as a normal baseball except that it deforms more severely during a collision. Why does this increased deformability lessen the forces exerted by the ball during a bounce and reduce the chances of its causing injury?
Greater distortion means a collision lasts longer, and impulse equals force times time.
You can do push-ups with either your toes or your knees acting as the pivot about which your body rotates. When you pivot about your knees, your feet can actually help you lift your head and chest. Explain.
If you lift your feet in the air, then the weight of your feet produces a torque which helps your body rotate.
When the brakes on his truck fail, the driver steers it up a runaway truck ramp. As the truck rolls up the ramp, it slows to a stop. What happens to the truck's kinetic energy, its energy of motion?
It converts into gravitational potential energy.
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.
Suppose you have gotten a new job where you have to design balls that fly through the air with as little resistance as possible. You know that in front of the ball there is laminar flow, so in back of the ball there should be
Laminar flow, so the leading and trailing pressure environments are similar.
Why does heat naturally flow from hot to cold?
Only that direction is statistically likely.
Railroad tracks must make only gradual curves to prevent trains from derailing at high speeds. Why is a train likely to derail if it encounters a sharp turn while it's traveling fast?
Sharp turn means a large horizontal acceleration means the apparent weight has a large horizontal component.
To keep as cool as possible while fighting a forest fire, what "color" clothes should you wear?
Silvery metallic
Why aren't there any thermometers that read temperatures down to -300 ºC?
That would be lower than absolute zero.
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.
You begin tossing the heavy rubber ball back and forth with a friend. When you toss it to your friend, the ball travels in an arc that peaks approximately midway between the two of you. Describe the ball's vertical motion, the component of its motion that lies along the vertical direction. (neglect air effects)
The ball's vertical motion is the same as that of a ball tossed upward to the same peak height. Both balls accelerate downward at the acceleration due to gravity and therefore rise more and more slowly, stop rising momentarily, and then descend more and more quickly.
You board an elevator with a large briefcase in your hand. Why does that briefcase suddenly feel particularly heavy when the elevator begins to move upward?
The briefcase is accelerating upward, so the resulting apparent weight is downward.
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
You have two golf balls that differ only in their surfaces. One has dimples on it while the other is smooth. If you drop these two balls simultaneously from a tall tower, which one will hit the ground first?
The dimpled ball.
Hurricanes are giant heat engines powered by the thermal energy in warm ocean regions and the order in colder surrounding areas. Why are hurricanes most violent when they form over regions of unusually hot water at the end of summer?
The energy difference between the hot and cold water is largest then, resulting in more energy available to power the storm.
If the bottom of your bicycle's front wheel becomes caught in a storm drain, your bicycle may flip over so that you travel forward over the front wheel. Explain this effect in terms of rotation, torque, and center of mass.
The force of the drain on the front wheel is very large and the direction of the force passes beneath the center of mass, so it produces an enormous torque rotating the bicycle forward.
If you are pulling a sled along a level field at constant velocity, how does the force you are exerting on the sled compare to the force of sliding friction on its runners?
The force you exert is equal to the sliding friction.
Suppose you are teaching a science course and have prepared a demonstration to teach how a thermometer works. When you plunge the thermometer into hot water, one of your students points out that the mercury in the thermometer actually went down a little bit before it shot up. It behaved in such a way because
The glass expanded before the mercury had a chance to, creating space.
Suppose you have two wool sweaters. Both sweaters are 1 cm thick but one weighs 50% more than the other. Which sweater provides you with the best insulation?
The lighter sweater is a better insulator
You are hired as an engineer at a thermometer factory. Suppose you built a water thermometer by replacing the mercury in a mercury thermometer with water. You want to measure temperatures above freezing with it. How would it behave as the temperature drops from 5oC to 1oC?
The reading will steadily increase
When an airplane's two engines are turning at almost the same rate, their combined sound can have a pulsing character to it. Explain that pulsing.
The sound waves from the two engines are alternately experiencing constructive and destructive interference.
When you mix milk or sugar into your coffee, you should move the spoon quickly enough to produce turbulent flow around the spoon. Why does this turbulence aid mixing?
The turbulence causes the coffee to move quickly in random directions, aiding mixing.
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.
A bread-making machine uses gears to reduce the rotational speed of its mixing blade. While its motor spins about 50 times each second, the blade spins only once each second. The motor provides a certain amount of work each second, so why does this arrangement of gears allow the machine to exert enormous forces on the bread dough?
The work done by the motor roughly equals the work done on the crankshaft, and work equals torque times angle rotated.
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
If you start two identical paper boats from the same point, you can make them follow the same path down a quiet stream. Why can't you do the same on a brook that contains eddies and vortices?
Turbulent water flows in unpredictacle directions.
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. What happens when you suck on the straw in order to bring water up?
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.
Which is more effective at heating a room:
a black woodstove
What fraction of the molecules in this room's air are water molecules?
about 2%
The cylinder contains a piece of paper. When I shove the plunger into the cylinder and compress the air suddenly, the paper will
burst into flames.
Those heat transfer mechanisms are
conduction: heat flows through materials convection: heat flows via moving fluids radiation: heat flows via electromagnetic waves
An open-open pipe has two open ends. If you open pipe has two open ends. If you close one end, making it an open close one end, making it an open-closed pipe, the closed pipe, the pitch of its fundamental vibration will
decrease by a factor of 2
You're sitting in a 150 °F sauna and are feeling F sauna and are feeling pretty hot. If you turn on the fan, you will feel
hotter than before.
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
It is a warm summer day and you are having lunch outdoors on a patio. A window air conditioning unit hums quietly nearby as it cools an office inside the building. Your friend notices that the unit's outdoor part is emitting a considerable amount of heat and comments on how strange that is. You explain correctly that the air conditioner's outside part is emitting the heat
it removes from the inside air and the heat it produces from the electricity it consumes.
Which temperature scale has 373 as the boiling point of water?
kelvins
Suppose you are standing on a bathroom scale when you are flying in a jet airplane. For a moment the scale reads less than your actual weight. During that moment, it's exerting an upward force on you that is
less than your weight.
A tapped wineglass emits a characteristic tone that decays gradually. To break a glass with sound, choose a glass with a decay time that's
long and expose it to its characteristic tone.
You float motionless in an inner tube, just far enough from the shore that the waves aren't breaking beneath you. You will
move in a circle as each wave passes, but make little or no progress toward shore
To get a pendulum swinging vigorously by giving it a series of small pushes, you should push it away from you each time it is
moving away from you
A car burns gasoline to obtain energy but allows some heat to escape into the air. Could a mechanically perfect car avoid releasing heat altogether?
no
If you heat the top of a fluid, will natural convection carry heat to the bottom of that fluid?
no
If you wrap aluminum foil around food, can you still warm it easily with infrared light?
no
You go to an amusement park and, being in a physics class, you have connections. The management lets you stand on a scale as you ride a Ferris Wheel that rotates fairly rapidly. You will notice the highest reading on the scale
on the bottom, because the normal force upwards is stronger than your weight.
At atmospheric pressure, ice can exist in thermal equilibrium
only at or below 0 °C (32 °F)
Melting is a _______ ______ that requires energy________ for the melting system.
phase transition; input
Suppose your car's speed doubles. By what factor will its kinetic energy change?
quadruple
If you double the mass of a pendulum, its period of oscillation of oscillation—the time it takes to complete one the time it takes to complete one full cycle of its motion full cycle of its motion—will
remain the same
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
At 100% relative humidity
steam and liquid water can coexist.
To convert thermal energy into work, some order must be consumed. The steam engine is consuming the order in
the hot steam and cold room air.
To convert thermal energy into work, some order must be consumed. Dipping duck is consuming the order in
the room's dry air and the duck's liquid water
For an object that sinks in a fluid,
the weight of fluid displaced is less than its weight.
For an object that is floating on a fluid,
the weight of the fluid displaced equals the object's weight.
For an object that is neutrally buoyant in a fluid,
the weight of the fluid displaced equals the object's weight.
As the moon orbits the earth, which way is the moon accelerating?
towards the earth
You have always wondered how much one of your friends weighs and devise a scheme to measure his weight secretly. You have him sit in a tubular steel chair. This popular style of chair consists of a single steel tube that is bent into a frame and that supports a seat bottom and a back. The empty chair weighs 10 pounds and is 30 inches tall. The frame acts as a spring and bends downward slightly when the chair is occupied. When you sit properly in the chair yourself, it bends downward 1 inch. When your friend sits properly in the chair, it bends downward 2 inches. From that observation, you know that your friend weighs about
twice as much as you do.
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,
we can't say anything until we know if the water on Mars is freshwater or not.
Can liquid water be heated above its boiling temperature?
yes
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 at you.
A bathroom scale reads:
your apparent weight
Suppose the earth's polar ice caps melted, sending water towards the equator and increasing the moment of inertia of the earth to 1.1 times its present value. The angular velocity of the earth will be
0.909 times its present value
Imagine that you are able to go on a fishing trip that you have always wanted to. Your friend gets a bite that exerts a force of about 50N on the pole and it bends by a certain amount. Now you have a pole identical to your friends and you get a hit that bends the pole about twice as much. You can estimate that the force on your pole is about:
100 N
Consider a wind turbine having moment of inertia 240,000 kg m2. If a 120 kg person were holding on to the edge of the turbine 10 m from its center the torque due to the person is ________ and the angular acceleration of the turbine is ________.
12,000 Nm; 0.005 rad/s2
A gymnast jumps upward with an initial speed of 10 m/s. She is in the air for a total time of about
2 seconds
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 sectional 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,
40 pounds.
A car starts from rest and accelerates at 4 m/s2. How much time will it take the car to reach a speed of 20 m/s?
5 s
Suppose your car is on a 5% grade, meaning that for every 100 m you travel along the road you raise or lower only 5 m in elevation. If your car weighs 1500 kg, what is the component of its weight parallel to the road?
750 N
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?
A reddish star
Why does an airplane have a "flight ceiling," a maximum altitude above which it can't obtain enough lift to balance the downward force of gravity?
Above that altitude the air density is too low to generate sufficient lift.
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 converts to kinetic energy (motion) of the fluid.
Which Law of Thermodynamics relates change in internal energy to heat added to a system and work done by it?
First
What two properties of a material affect the speed of sound in the material?
Density and stiffness.
A quality perfume is a mixture of essential oils and has a scent that changes with time and skin temperature. Explain the gradual change of the perfume's scent with time in terms of evaporation.
Different oils in the perfume evaporate at different rates
Why are good thermal conductors generally good electric conductors also?
Electron motion is responsible for determining both properties.
Which of the following quantities is not conserved?
Entropy
If you submerge a 7-kg log in water and it displaces 11 kg of water, what will the net force on the log be the moment you let go of the log?
F = 39.2 N
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.
Why does an ice cube feel cold?
Heat from your hand enters the cube by conduction
If you were laying steel track for a railroad, what influence would thermal expansion have on your work?
I would need to account for the steel rail changing its size as the temperature rises and falls.
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 claim is impossible.
If there is no heat release, then heat in equals work out and the engine is 100% efficient, which violates the second law of thermodynamics.
Suppose your car is traveling at a certain speed on a very slick road. All of a sudden you step on the accelerator and the back wheels begin to spin but the car remains at the same speed. The kinetic energy of the car
Increases because of the increased rotation of the tires
When you throw a hot rock into a cold puddle, what happens to the overall entropy of the system?
It increases.
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.
An icy sidewalk gradually loses its ice even when the weather stays cold. Where does the ice go?
It sublimes into the air.
If you are backing up but slowing down, your acceleration is directed:
forwards
Your body is presently converting chemical potential energy from food into 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.
Which temperature scale has 373 as the boiling point of water?
Kelvin
When a fish hovers over the bottom of a lake, what forces act on it, and what is the net force?
Lift and weight, for a net force zero
Who invented the internal combustion engine?
Otto
What does a heat pump not do?
Perform work on its surroundings
Use the concept of convection to explain why firewood burns better when it's raised above the bottom of a fireplace on a grate.
Raising the wood allows convection to cause air to circulate around the wood, giving it more oxygen.
Suppose a water wave strikes a very large solid barrier, such as a cliff. Through which of the following will the wave redirect its motion?
Reflection
"The entropy of an isolated system never decreases." Which Law of Thermodynamics is this?
Second
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.
Why do bridges have special gaps at their ends to allow them to change lengths?
Temperature changes will cause the bridge to expand and contract.
What prevents the bottom half of a glass of water from spontaneously freezing while the top half becomes boiling hot?
That would violate the law of entropy.
An acorn falls from a branch located 9.8 m above the ground. After 1 s of falling, the acorn's velocity will be 9.8 m/s downward. Why hasn't the acorn hit the ground?
The acorn's average speed for the 1 s is less than 9.8 m/s.
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.
A marshmallow is filled with air bubbles. Why does a marshmallow puff up when you toast it?
The air in the bubbles gets warm and expands.
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.
When a star runs out of nuclear fuel, gravity may crush it into a neutron star about 20 km (12 miles) in diameter. Although the star may have taken a year or so to rotate once before its collapse, the neutron star rotates several times a second. Explain this dramatic increase in angular velocity.
The angular momentum of the star is conserved.
The molecules of antifreeze dissolve easily in water. Why does adding antifreeze to the water in a car radiator keep the water from freezing in the winter and boiling in the summer?
The antifreeze lowers the freezing temperature and raises the boiling temperature of the water
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 boiling point of water is much lower at very low pressure.
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 salad cold longest?
The foil side
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.
The air near a woodstove circulates throughout the room. What provides the energy needed to keep the air moving?
The heat from the fire in the woodstove.
A difficult-to-open jar may open easily after being run under hot water for a moment. Explain.
The heat from the water makes the lid expand and loosen.
If you remove ice cubes from the freezer with wet hands, the cubes often freeze to your fingers. How can the ice freeze the water on your hands? Shouldn't they melt instead?
The ice cubes are well below 0 °C, so they can pull heat from the water on your hands before they start to melt.
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.
You can use a blender to crush ice cubes, but if you leave it churning too long, the ice will melt. What supplies the energy needed to melt the ice?
The kinetic energy of the blender blades
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.
You are hired as an engineer at a thermometer factory. Suppose you built a water thermometer by replacing the mercury in a mercury thermometer with water. You want to measure temperatures above freezing with it. How would it behave as the temperature drops from 5o C to 1o C?
The reading will decrease and then begin increasing
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 releases more energy as heat than it removes from the air inside itself.
Explain how convection contributes to the shape of a candle flame.
The rising warm air causes the flame to elongate upward.
On a bitter cold day, the snow is light and powdery. This snow doesn't begin melting immediately when you bring it into a warm room. Why?
The snow's temperature needs to rise to 0 °C before it can start melting.
If you stand in front of a stone building and clap your hands, you hear an echo. What is happening to the sound wave to cause this echo?
The sound wave is being reflected by the stone surface.
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.
You whistle twice, sending out two sound waves. Can you make the second sound wave overtake the first and, if so, how?
no
Sound can pass from one paper cup to another through a long, taut string that connects their bottoms. What type of wave is present in the string when your voice shakes the bottom of your cup in and out and your friend hears your voice from the other cup.
The string has a longitudinal traveling wave.
Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun sets near the seashore.
The surface wind will blow from the land toward the water
Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun rises near the seashore.
The surface wind will blow from the water toward the land.
Waves tend to bend toward points of land projecting into the ocean and erode those points. What causes the wave to bend toward the points?
The waves slow down as they enter shallow water and refraction bends them toward the shore.
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.
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.
Suppose someone claimed to have a device that could convert heat from the room into electric power continuously. You would know that this device was a fraud because it would violate the second law of thermodynamics. Explain.
This device would be decreasing the entropy of the universe.
Why does it take longer to cook pasta properly in boiling water in Denver (the "mile-high city") than it does in New York City?
Water has a lower boiling temperature in Denver than in New York.
Musical tones can linger for many seconds in a stone cathedral. Why?
When a sound wave attempts to move from air to stone, it reflects almost perfectly.
When you fly a kite, there is a time when you must do (positive) work on the kite. Is that time when you let the kite out or when you pull it in?
When you pull the kite in.
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
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
atmospheric pressure cannot support a column of lemonade 20 meters tall.
The first law of thermodynamics is a re - statement of the law of _________________.
conservation of energy
You construct a water-powered go-cart by attaching a large tank of water to a cart. The water can be forced out a nozzle by connecting a tank of high-pressure air to the water tank. In preparation for your first ride, you position this contraption facing away from a brick wall. You climb on and start spraying the water against the wall. To your delight you accelerate away from the wall and begin to move. When you have moved far enough away from the wall that the stream of water can no longer hit it, you
continue to accelerate as the water sprays out the back of the cart.
Wind is one of nature's ways of transferring energy through
convection
Ice is ___________.
crystalline
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?
he relative humidity of the air in the bag reaches 100%.
Skateboarders often can skate on the inner surface of cylindrical or bowl - shaped tracks. As a result, the normal (support) force is able to point inwards towards the center of the circle wherever the person is. That center-directed or centripetal force on the skate wheels is important because it
helps the skater accelerate inward to complete each turn without skidding.
When a Frisbee is flying horizontally through the air, the speed of the air flowing over the Frisbee's top is
higher than the speed of the air beneath it and the pressure on top of the Frisbee is less than the pressure beneath it.
The "strokes", or "cycles" in a four - stroke engine are ____________________.
induction, compression, power, exhaust
A shiny, white transparent surface prevents heat transfer because
it has emissivity of zero and reflects all light that strikes it.
You next begin exercising with a heavy rubber ball. You throw the ball straight up, high above your head, and then catch it as it descends. At the moment the ball reaches its peak height above your head, (neglect any effects due to the air)
its acceleration is constant and its velocity is changing with time
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
no heat will flow between any parts.
A pedestrian bridge crosses a street. This bridge is entirely supported by columns from 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
Freezing is a ____________ that requires energy ________ for the melting system.
phase transition; release
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 fire fighter and the aluminum tent reflects most of that radiation.
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.
Suppose you are driving north and suddenly hit your brakes to avoid a dog in the road. As you come to a stop your acceleration is directed:
south
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.
Some scientists assert that there would be no life on earth if ice did not have a molecular structure with a lot of open space because
the density of ice would be greater than water and lakes would freeze solid - from the bottom up.
Housing and natural animal insulation works because
the insulating materials trap air and prevent convection.
When cooking a potato in a conventional oven it is useful to stick a nail in it, which makes it cook faster. This is because
the nail is a good conductor of heat.
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,
the pressure of the fluid in the needle and much larger syringe are the same.
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
When you pour honey into a bowl, it flows smoothly. If you did the same with water, it would splash. These different behaviors occur because honey's high
viscosity keeps it flowing smoothly while water's low viscosity allows inertia to break its flow into many separate pieces.
A common glass thermometer contains a red or silver liquid that rises upward in a glass tube as the temperature of the thermometer increases. The liquid moves up the tube because
while both the glass and the liquid expand as their temperatures increase, the liquid expands more rapidly than the glass does.
A speedboat is pulling a water-skier with a rope, exerting a large forward force on her. The skier is traveling in a straight line at constant speed. The net force she experiences is
zero
You are done with the barbell, so you hold it at chest height and walk across the level floor to the storage rack. As you walk at constant velocity toward the rack, what work are you doing on the barbell?
zero work