How Things Work Final - All Problem Sets

The steel ball in a pinball game rolls around a flat, tilted surface. If you flick the ball straight uphill, it gradually slows to a stop and then begins to roll downhill. Which direction is the ball accelerating (a) as it rolls uphill? (b) as it rolls downhill? - (a) downhill; (b) uphill - (a) downhill; (b) downhill - (a) zero; (b) downhill - (a) uphill; (b) downhill

- (a) downhill; (b) downhill

A metro train is traveling at constant velocity. What are the net forces on (a) the first car, (b) the middle car, and (c) the last car? - (a) zero; (b) zero; (c) zero - (a) backward; (b) zero; (c) forward - (a) forward; (b) forward; (c) forward - (a) forward; (b) zero; (c) backward

- (a) zero; (b) zero; (c) zero

Your suitcase weighs 50 N. As you ride up an escalator toward the second floor, carrying that suitcase, you are traveling at a constant velocity. The upward force you must exert on the suitcase to keep it moving with you is - depends on the speed of the escalator. - less than 50 N. - greater than 50 N. - 50 N.

- 50 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 downward. - 850 N upward - less than 850 N upward - 0 N

- 850 N upward

Winds are driven by differences in temperature at the earth's surface. Air rises over hot spots and descends over cold spots, forming giant convection cells of circulating air. Near the ground, winds blow from the cold spots toward the hot spots. Explain how the atmosphere is acting as a heat engine. - A heat engine is a device that converts thermal energy into ordered energy as heat flows from a hot object to a cold object. The rising warm air moves into colder areas and creates ordered energy in the form of the winds, thus fulfilling the definition of a heat engine. - A heat engine is a device that converts thermal energy into ordered energy as heat flows from a cold object to a hot object. The wind moves from a hot area into a cold area, thus fulfilling the definition of a heat engine. - A heat engine is a device that converts thermal energy into ordered energy as heat flows from a hot object to a cold object. The wind moves from a hot area into a cold area, thus fulfilling the definition of a heat engine. - A heat engine is a device that converts thermal energy into ordered energy as heat flows from a cold object to a hot object. The rising warm air moves into colder areas and creates ordered energy in the form of the winds, thus fulfilling the definition of a heat engine.

- A heat engine is a device that converts thermal energy into ordered energy as heat flows from a hot object to a cold object. The rising warm air moves into colder areas and creates ordered energy in the form of the winds, thus fulfilling the definition of a heat engine.

There have been baseball seasons in which so many home runs were hit that people began to suspect that something was wrong with the baseballs. What change in the baseballs would account for them traveling farther than normal? - Using springier bats. - A higher spring constant. - A more rubbery surface. - A higher coefficient of restitution.

- A higher coefficient of restitution.

A yo-yo is a spool-shaped toy that spins on a string. In a sophisticated yo-yo, the end of the string forms a loop around the yo-yo's central rod rod so that the yo-yo can spin almost freely at the end of the string. Why does the yo-yo spin longest if the central rod is very thin and very slippery? - The center of mass of the yo-yo is in the middle of the central rod. - A thin and slippery rod minimizes friction between the rod and string. - This maximizes the yo-yo's angular momentum. - A thin and slippery rod makes a large torque.

- A thin and slippery rod minimizes friction between the rod and string.

Why does snow blanket the ground almost uniformly rather than creating tall piles in certain areas and bare spots in others? - Tall piles and bare spots would violate the first law of thermodynamics. - A uniform blanket has higher entropy than tall piles and bare spots. - Tall piles and bare spots would violate the law of conservation of energy. - Tall piles and bare spots would violate the law of thermal equilibrium.

- A uniform blanket has higher entropy than tall piles and bare spots.

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 is too cold to generate sufficient lift. - Above that altitude the air pressure is too low to generate sufficient lift. - Above that altitude the air density is too low to generate sufficient lift. - Above that altitude there isn't enough air to generate sufficient lift.

- Above that altitude the air density is too low to generate sufficient lift.

Why do aluminum pans heat food much more evenly than stainless steel pans when you cook on a stove? - Aluminum has a much lower latent heat of fusion than stainless steel. - Aluminum has a much higher specific heat than stainless steel. - Aluminum has a much lower specific heat than stainless steel. - Aluminum has a much higher thermal conductivity than stainless steel.

- Aluminum has a much higher thermal conductivity than stainless steel.

While a gymnast is in the air during a leap, which of the following quantities must remain constant for her: velocity, momentum, angular velocity, or angular momentum? - All four - Both momentum and angular momentum - Momentum only - Angular momentum only

- Angular momentum only

As you swing back and forth on a playground swing, your apparent weight changes. At what point do you feel the heaviest? - At the lowest point of your swing. - In the middle of your swing going forward, but not yet at the lowest point. - At the top of your swing going either forward or backward. - At the top of your swing going backward.

- At the lowest point of your swing.

When you apply the brakes on your bicycle, which way do you accelerate? - You don't accelerate, you decelerate. - Forward. - Backward. - You don't accelerate; that would be speeding up.

- Backward.

A flute and a piccolo are both effectively pipes that are open at both ends, with holes in their sides to allow them to produce more tones. The piccolo is very nearly a half-size version of the flute. How does this fact explain why the piccolo's tones are one octave above those of a flute? - Because the metal tube of a piccolo is half the diameter of a flute's metal tube, the piccolo tube vibrates at twice the pitch of the flute tube. - Because the metal tube of a piccolo is half the length of a flute's metal tube, the piccolo tube vibrates at twice the pitch of the flute tube. - Because the air column inside a piccolo is half as wide as the air column inside a flute, it vibrates at twice the pitch of the flute's vibrations. - Because the air column inside a piccolo is half the length of the air column inside a flute, it vibrates at twice the pitch of the air column inside a flute.

- Because the air column inside a piccolo is half the length of the air column inside a flute, it vibrates at twice the pitch of the air column inside a flute.

The most important difference between a trumpet and a tuba is in the lengths of their pipes: the tuba's pipe is much longer than that of the trumpet. Why is the tuba's fundamental vibrational frequency much lower than that of the trumpet? - Because the air column inside the tuba is much longer than that inside the trumpet, it has more mass and less stiffness than the trumpet's air column. - Because the tuba's metal pipe is longer than the trumpet's pipe, it has more mass and more stiffness than the trumpet's pipe. - Because the air column inside the tuba is much longer than that inside the trumpet, it has more mass and more stiffness than the trumpet's air column. - Because the tuba's metal pipe is longer than the trumpet's pipe, it has more mass and less stiffness than the trumpet's pipe.

- Because the air column inside the tuba is much longer than that inside the trumpet, it has more mass and less stiffness than the trumpet's air column.

Why are black steam radiators better at heating a room than radiators that have been painted white or silver? - Black is the hottest color. - Black absorbs heat better than white. - Air circulates better with a black radiator. - Black is the best color for emitting thermal radiation.

- Black is the best color for emitting thermal radiation.

When you kick a soccer ball, which pushes on the other harder: your foot or the soccer ball? - The soccer ball pushes harder. - The answer depends on additional factors not mentioned here. - Your foot pushes harder. - Both push equally.

- Both push equally.

Which action will give you more momentum toward the north: throwing one shoe southward at 10 m/s or two shoes southward at 5 m/s? - One shoe southward at 10 m/s. - Two shoes southward at 5 m/s. - Additional information is needed. - Both will give the same momentum.

- Both will give the same momentum.

If you sit in a good swivel chair with your feet off the floor, the chair will turn slightly as you move about but will immediately stop moving when you do. Why can't you make the chair spin without touching something? - Changing a system's angular momentum requires an angular impulse. - Actually, you can if you jerk yourself hard enough. - Changing a system's energy requires work. - Changing a system's momentum requires an impulse.

- Changing a system's angular momentum requires an angular impulse.

Waterproof watches have a maximum depth to which they can safely be taken while swimming. Why? - Because taking it to too great a depth would void the warranty on the watch. - Deeper than that depth the air pressure is so great it might damage the watch. - Deeper than that depth the water pressure is so great it might damage the watch. - Deeper than that depth the air pressure inside the watch might cause the watch to burst.

- Deeper than that depth the water pressure is so great it might damage the watch.

A favorite college prank involves simultaneously flushing several toilets while someone is in the shower. The cold water pressure to the shower drops and the shower becomes very hot. Why does the cold water pressure suddenly drop? - Flushing increases the water pressure at the toilets, lowering the pressure at the shower. - The cold water is diverted from the shower to the toilets. - Actually, the flushing increases the hot water pressure rather than lowering the cold water pressure. - Flushing makes the water in the pipes flow faster, dropping the pressure.

- Flushing makes the water in the pipes flow faster, dropping the pressure.

When you're driving on a level road and there's ice on the pavement, you hardly notice that ice while you're heading straight at a constant speed. Why is it that you only notice how slippery the road is when you try to turn left or right, or to speed up or slow down? - The heavier the car is, the greater the friction between the tires and the road. - Friction between the tires and the road is reduced when the road is icy. - Friction is only required when you try to change the car's velocity. - The force of the car's inertia keeps it going.

- Friction is only required when you try to change the car's velocity.

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. - The ball is 30% warmer. - The ball loses 30% of its kinetic energy. - Gravitational potential energy is proportional to height. - 30% of the energy is lost.

- 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. - This is not true. The dropped ball will hit the ground first. - Gravity acts only in the vertical direction. - The earth's curvature beneath the bullet compensates for its slower time of fall. - This is not true. The bullet will hit the ground first.

- Gravity acts only in the vertical direction.

People falling from a high diving board feel weightless. Has gravity stopped exerting a force on them? If not, why don't they feel it? - Gravity no longer exerts a force on them while they're falling. - Gravity still exerts a force on them, but they don't feel it because they're falling. - Gravity still exerts a force on them, but they don't feel it because their apparent weight has become zero. - Gravity still exerts a force on them, but they don't feel it because of air resistance.

- Gravity still exerts a force on them, but they don't feel it because their apparent weight has become zero.

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? - The RIF ball is softer but just as bouncy. - The RIF ball has a smaller spring constant. - Greater distortion means a collision lasts longer, and impulse equals force times time. - The energy is less in an RIF ball.

- Greater distortion means a collision lasts longer, and impulse equals force times time.

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. - Greater pressure makes the water come out harder. - Greater pressure means more water comes out. - Greater pressure means the water arrives sooner.

- Greater water pressure means the water emerges from the hoses faster, so it can spray farther.

A diver leaps from a 50-m cliff into the water below. The cliff is not perfectly vertical, so the diver must travel forward several meters in order to avoid the rocks beneath him. What is the best way for the diver to leap in order to miss the rocks? - He should leap straight up. - He should leap forward. - It does not matter how he leaps. - He should leap straight down.

- He should leap forward.

Why would replacing the air inside a metal organ pipe with helium gas raise the pipe's pitch? - Helium has a lower pressure than air, so it allows the metal pipe to vibrate more rapidly. - Helium lowers the total mass of the organ pipe so that metal pipe can vibrate more rapidly. - Helium is less dense than air, so it accelerates more rapidly than air. - Helium has a lower pressure than air, so it accelerates more rapidly than air.

- Helium is less dense than air, so it accelerates more rapidly than air.

Why can't an acrobat stop himself from spinning while he is in midair? - His energy is conserved. - His angular momentum is conserved. - Actually, he can. All he has to do is straighten out his body. - His momentum is conserved.

- His angular momentum is conserved.

In the Mediterranean Sea, high tide is only 30 cm above low tide. Why? - The Mediterranean Sea is relatively shallow and it therefore contains too little water to develop large tides. - The Mediterranean Sea is relatively close to the Equator, where the tidal bulges are particularly weak. Its tides would be much larger if it were nearer the North Pole. - If one end of the Mediterranean Sea is at high tide, then the other end is at low tide. Those tides are too close together to have large differences in height. - The Mediterranean Sea is relatively warm and it is too buoyant to develop large tides.

- If one end of the Mediterranean Sea is at high tide, then the other end is at low tide. Those tides are too close together to have large differences in height.

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 it's in the middle it must be swimming, no matter how slowly. - Dead fish generally float to the top of the water. - If the fish is floating at a middle height, it must be be regulating its density to be equal to the density of the water, which a dead fish couldn't do. - Live fish can control their position in the water.

- If the fish is floating at a middle height, it must be be regulating its density to be equal to the density of the water, which a dead fish couldn't do.

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. - Your feet pushing against the ground produces a torque which helps your body rotate. - Your feet resting on the ground means there is less weight to lift. - Your feet help anchor your knees so they don't slip.

- If you lift your feet in the air, then the weight of your feet produces a torque which helps your body rotate.

Astronauts learn to tolerate weightlessness by riding in an airplane (nicknamed the "vomit comet") that follows an unusual trajectory. How does the pilot direct the plane in order to make its occupants feel weightless? - In a curve that follows the path of a thrown object with only gravity exerting a force on it. - In an upside-down circular curve. - In a clothoid curve like that of a roller-coaster loop. - Straight up then straight down.

- In a curve that follows the path of a thrown object with only gravity exerting a force on it.

It's easier to injure your knees and legs while hiking downhill than while hiking uphill. Use the concept of energy to explain this observation. - You have more gravitational potential energy at the top the hill than at the bottom. - You have more kinetic energy going downhill than uphill because you're moving faster. - In going downhill, your knees and legs have work done on them as they absorb gravitational potential energy. In going uphill, your knees and legs do work to overcome gravitational potential energy. - It takes more energy to go uphill than downhill.

- In going downhill, your knees and legs have work done on them as they absorb gravitational potential energy. In going uphill, your knees and legs do work to overcome gravitational potential energy.

Some amusement park rides move you back and forth in a horizontal direction. Why is this motion so much more disturbing to your body than cruising at a high speed in a jet airplane? - In the ride you're exposed to the moving air, whereas in the jet you're in a sealed box. - The effect is entirely psychological. - In the ride your feeling of acceleration is constantly changing, whereas in the jet you have no feeling of acceleration. - Side-to-side motion is more disturbing than forward/back motion.

- In the ride your feeling of acceleration is constantly changing, whereas in the jet you have no feeling of acceleration.

Firefighters slide down a pole to get to their trucks quickly. What happens to their gravitational potential energy, and how does it depend on the slipperiness of the pole? - It is turned into work. A slippery pole makes this happen more quickly. - It converts to kinetic energy and thermal energy of their hands and the pole. A slippery pole will result in more kinetic and less thermal energy. - It converts to kinetic energy and heat energy. A slippery pole will result in more kinetic and less heat energy. - It is lost as they come to a stop. A slippery pole makes it get lost more quickly.

- It converts to kinetic energy and thermal energy of their hands and the pole. A slippery pole will result in more kinetic and less thermal energy.

Some of the strings in a piano are made of steel wire wrapped with a spiral of copper wire. The copper wire doesn't contribute to the tension in the string, so what is its purpose? - It increases the mass of the string, thereby raising the string's pitch. - It decreases the mass of the string, thereby lowering the string's pitch. - It decreases the mass of the string, thereby raising the string's pitch. - It increases the mass of the string, thereby lowering the string's pitch.

- It increases the mass of the string, thereby lowering the string's pitch.

When you throw a hot rock into a cold puddle, what happens to the overall entropy of the system? - More information is needed. - It remains constant. - It increases. - It decreases.

- It increases.

A tuning peg slips on your violin, lessening the tension in one of the strings. What effect does this change have on the string's sound? - It decreases the volume of the string, but has no effect on the string's pitch. - It raises the pitch (vibrational frequency) of the string. - It increases the volume of the string, but has no effect on the string's pitch. - It lowers the pitch (vibrational frequency) of the string.

- It lowers the pitch (vibrational frequency) of the string.

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 warms up. - It melts some of the ice. - It is absorbed. - It cools off.

- 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 is absorbed. - It melts some of the ice. - It cools off. - It heats up.

- 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 melts. - It dissolves. - It evaporates into the surrounding air. - It sublimes into the surrounding air.

- It sublimes into the surrounding air.

Falling into a leaf pile is much more comfortable than falling onto the bare ground. In both cases you come to a complete stop, so why does the leaf pile feel so much better? - The soft leaves cushion your fall. - It takes more time to come to rest falling in a leaf pile, so the stopping force is less. - The stopping time for hitting the ground is bigger. - Hitting the ground involves a bigger impulse than hitting the leaves.

- It takes more time to come to rest falling in a leaf pile, so the stopping force is less.

A helium-filled balloon floats in air. What will happen to an air-filled balloon in helium? Why? - It will sink because air is denser than helium. - It will rise because helium is less dense than air. - It will sink because helium is denser than air. - It will neither rise nor sink because air and helium are both gases.

- It will sink because air is denser than helium.

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. - More information is needed to be able to answer. - It would remain constant. - It would increase.

- It would decrease.

Why does hot maple syrup pour more easily than cold maple syrup? - Its Reynolds number increases at higher temperatures. - Its viscosity is higher at higher temperatures. - Its Reynolds number decreases at higher temperatures. - Its viscosity is lower at higher temperatures.

- Its viscosity is lower at higher temperatures.

Tightrope walkers often use long poles for balance. Although the poles don't weigh much, they can exert substantial torques on the walkers to keep them from tipping and falling off the ropes. Why are the poles so long? - Long poles are easier to balance. - Longer poles weigh more. - Longer poles are just part of the showmanship of tightrope-walking. - Longer poles mean larger torques.

- Longer poles mean larger torques.

In countless movie and television scenes, the hero punches a brawny villain who doesn't even flinch at the impact. Why is the immovable villain a Hollywood fantasy? - Angular momentum must be conserved. - Momentum must be conserved. - Energy must be conserved. - The impulse of the hero's fist is greater than the impulse of the villain's jaw.

- Momentum must be conserved.

Why does a pot of water heat up and begin boiling more quickly if you cover it? - Covered pots boil more quickly. - No heat is being carried away by evaporating water. - The lid traps the heat. - The lid makes the pressure go up.

- No heat is being carried away by evaporating water.

As you jump across a small stream, does a horizontal force keep you moving forward? If so, what is the force? - Yes, there is a horizontal force. Inertia is that force. - Yes, there is a horizontal force. Gravity is that force. - Yes, the horizontal force of the leap pushes you across the stream. - No, there is no horizontal force. You continue to move forward because of inertia.

- No, there is no horizontal force. You continue to move forward because of inertia.

Why does it hurt less to land on a soft foam pad than on bare concrete after completing a high jump? - Padding means greater distortion means the collision lasts longer, and impulse equals force times time. - The foam pad has a smaller spring constant. - The foam pad is softer. - The energy is less in a foam pad.

- Padding means greater distortion means the collision lasts longer, and impulse equals force times time.

During rehabilitation after hand surgery, patients are often asked to squeeze and knead putty to strengthen their muscles. How does the energy transfer in squeezing putty differ from that in squeezing a rubber ball? - Putty absorbs energy from the hands. - It takes more energy to squeeze a rubber ball than to squeeze putty. - Putty converts the energy of the squeeze into thermal energy, whereas the rubber ball returns the energy to the hand. - It takes more energy to squeeze putty than to squeeze a rubber ball.

- Putty converts the energy of the squeeze into thermal energy, whereas the rubber ball returns the energy to the hand.

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? - The moving air carries the moisture off. - Relative humidity drops with rising temperature. - Cold air is wetter than warm air. - Hot air is drier than cold air.

- Relative humidity drops with rising temperature.

Describe the process of writing with chalk on a blackboard in terms of friction and wear. - Sliding friction between chalk and blackboard causes wear on the chalk. - There is friction between the chalk and blackboard, and if you get chalk dust on your clothes you'll have to wear it. - Chalk dust is left wear there is friction with the blackboard. - Static friction between chalk and blackboard causes wear on the chalk.

- Sliding friction between chalk and blackboard causes wear on the chalk.

A common pair of pliers has a place for cutting wires, bolts, or nails. Why is it so important that this cutter be located very near the pliers' pivot? - Small lever arm means large force. - Small lever arm means large torque. - Close to the pivot there is less friction. - The cutter has a large lever arm.

- Small lever arm means large force.

Why aren't there any thermometers that read temperatures down to -300 ºC? - Making a thermometer to read that low would be prohibitively expensive. - There is no substance that remains liquid at that low a temperature. - That would be lower than absolute zero. - There are; they are just extremely expensive.

- That would be lower than absolute zero.

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 conservation of energy. - That would violate the law of thermal equilibrium. - That would violate the first law of thermodynamics. - That would violate the law of entropy.

- That would violate the law of entropy.

Comic book superheroes often catch a falling person only a hairsbreadth from the ground. Why would this rescue actually be just as fatal for the victim as hitting the ground itself? - It is the fall that kills a person, not how they stop. - The acceleration required to stop in such a short time is still huge, so the force required would be huge. - A superhero's arms are as hard as the ground. - This is incorrect. The falling person has a much better chance of surviving if the superhero catches her.

- The acceleration required to stop in such a short time is still huge, so the force required would be huge.

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? - This is incorrect. The acorn has hit the ground after 1 s of fall. - Air resistance held it back. - The acorn's average speed for the 1 s is less than 9.8 m/s. - The gravity is weaker farther from the earth, so it wasn't going fast enough when it started falling.

- The acorn's average speed for the 1 s is less than 9.8 m/s.

Explain why a parachute slows your descent when you leap out of an airplane. - The air flow around the parachute is turbulent with a small turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity. - The air flow around the parachute is turbulent with a large turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity. - The air flow around the parachute is turbulent with a small turbulent wake, leading to huge viscous drag forces and a relatively small terminal velocity. - The air flow around the parachute is turbulent with a large turbulent wake, leading to huge viscous drag forces and a relatively small terminal velocity.

- The air flow around the parachute is turbulent with a large turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity.

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 at 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. - The air inside is more dense than the air outside. When the lid is opened, the densities equalize, and the dimple pops back to its normal position. - The air inside is less dense than the air outside. When the lid is opened, the densities equalize, and the dimple pops back to its normal position. - The air inside the jar is at higher pressure than the air outside, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position.

- The air outside is at 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 gets more dense as it gets colder. - The air pressure of the air outside the container pushes the lid in. - The hot food shrinks as it cools. - The weight of the lid makes it bow inward.

- The air pressure of the air outside the container pushes the lid in.

A poorly designed household fan stalls, making it inefficient at moving air. Describe the airflow through the fan when its blades stall. - The airflow is generating shock waves. - The airflow is laminar rather than turbulent. - The airflow is turbulent rather than laminar. - The airflow is shedding vortices.

- The airflow is turbulent rather than laminar.

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 energy of the star is conserved. - The momentum of the star is conserved. - The nuclear energy of the star does work to speed the star up. - The angular momentum of the star is conserved.

- The angular momentum of the star is conserved.

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 downward, so the resulting apparent weight is upward. - The briefcase is accelerating downward, so the resulting apparent weight is downward. - The briefcase is accelerating upward, so the resulting apparent weight is upward. - The briefcase is accelerating upward, so the resulting apparent weight is downward.

- The briefcase is accelerating upward, so the resulting apparent weight is downward.

How does a crowbar make it easier to lift the edge of a heavy box a few centimeters off the ground? - The long handle of the crowbar is easier to grip. - The force of your hand on the crowbar is equal to the force of the crowbar on the box. - The lever arm of your hand on the crowbar is equal to the lever arm of the crowbar on the box. - The crowbar has a large lever arm compared to the lever arm of the crowbar on the box on the lid, so the force exerted on the handle is magnified.

- The crowbar has a large lever arm compared to the lever arm of the crowbar on the box on the lid, so the force exerted on the handle is magnified.

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? - Whichever ball is heavier. - Both will hit simultaneously. - The dimpled ball. - The smooth ball.

- 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? - By the end of the summer, more thermal energy has built up in the water. - A heat enegine produces ordered energy as heat moves from a hot region to a colder region. - The hot water contains more energy than the cold water - The energy difference between the hot and cold water is largest then, resulting in more energy available to power the storm.

- The energy difference between the hot and cold water is largest then, resulting in more energy available to power the storm.

A horse does work on a cart it's pulling along a straight, level road at a constant speed. The horse is transferring energy to the cart, so why doesn't the cart go faster and faster? Where is the energy going? - The energy is lost. - The energy is going to maintain the speed of the cart. - The energy is converted to thermal energy as the wheels, axles, and ground get warmer. - The energy is converted to gravitational potential energy of the cart.

- The energy is converted to thermal energy as the wheels, axles, and ground get warmer.

The best running tracks have firm but elastic rubber surfaces. How does a lively surface assist a runner? - The track surface increases the runner's coefficient of restitution. - The runner's feet don't lose their energy. - A very lively surface will have a coefficent of restituion greater than 1 - The energy of the collisions between the runner's feet and the track surface is largely not lost, but returned to the runner.

- The energy of the collisions between the runner's feet and the track surface is largely not lost, but returned to the runner.

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 less than the sliding friction. - There is no set relationship between the two forces. - The force you exert is equal to the sliding friction. - The force you exert is greater than the sliding friction.

- The force you exert is equal to the sliding friction.

Which is larger: the force the earth exerts on you or the force you exert on the earth? - The earth's force on you is larger. - Your force on the earth is larger. - The forces are equal. - The answer depends on additional factors not mentioned here.

- The forces are equal.

Skiers often stop by turning their skies sideways and skidding them across the snow. How does this trick remove energy from a skier, and what happens to that energy? - The friction of skidding converts the skier's energy into kinetic energy of the snow flying into the air. - The friction of skidding converts the skier's energy into thermal energy. - The friction of skidding causes the skier's energy to be lost. - The friction of skidding converts the skier's energy into gravitational potential energy of the snow flying into the air.

- The friction of skidding converts the skier's energy into thermal energy.

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? - Pressure decreases as the height of the tea decreases. - There is less tea, so it comes out slower. - As the container empties the air inside expands to fill the volume of the container, creating a suction effect which slows the tea coming out. - The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.

- The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.

Why must tall dams be so much thicker at their bases than at their tops? - The pressure is greater at the bottom due to greater pressure at the top. - The greater the depth of the water the greater the pressure pushing on the wall of the dam. - The pressure is greater at the bottom due to greater kinetic energy per volume at the top. - A tall dam needs a lot of structural support.

- The greater the depth of the water the greater the pressure pushing on the wall of the dam.

When a sharpshooter fires a pistol at a target, the gun recoils backward very suddenly, leaping away from the target. Explain this recoil effect in terms of the transfer of momentum. - The gun transfers (forward) momentum to the bullet, so the bullet transfers equal (backward) momentum to the gun. - The gun transfers (forward) momentum to the bullet, so the gun recoils. - The gun's recoil is the reaction to the forward momentum of the bullet. - The bullet transfers (backward) momentum to the gun.

- The gun transfers (forward) momentum to the bullet, so the bullet transfers equal (backward) momentum to the gun.

A jar-opening tool grabs onto a jar's lid and then provides a long handle for you to turn. Why does this handle's length help you to open the jar? - The force of your hand on the handle is equal to the force of the tool on the lid. - A long handle is easier to grip. - The handle has a large lever arm compared to the lever arm of the tool on the lid, so the force you exert on the handle is magnified. - The lever arm of your hand on the handle is equal to the lever arm of the tool on the lid.

- The handle has a large lever arm compared to the lever arm of the tool on the lid, so the force you exert on the handle is magnified.

The space shuttle generates thermal energy during its operation in earth orbit. How is it able to get rid of that thermal energy as heat in an airless environment? - The heat is conducted off by the vacuum. - The heat leaves the shuttle as thermal radiation. - The heat leaves the shuttle as thermal energy. - The heat is convected off by the vacuum.

- The heat leaves the shuttle as thermal radiation.

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 melt a little, then all the water freezes. - The ice cubes are well below 0 °C, so they can pull heat from the water on your hands before they start to melt. - The ice is colder than the water. - The water from your hands freezes onto the ice cubes.

- The ice cubes are well below 0 °C, so they can pull heat from the water on your hands before they start to melt.

You can inflate a plastic bag by holding it up so that it catches the wind. Use Bernoulli's equation to explain this effect. - The potential energy of the moving air converts into greater air pressure inside the bag, which inflates the bag. - The air blows up the bag. - The pressure of the moving air converts into greater air pressure inside the bag, which inflates the bag. - The kinetic energy of the moving air converts into greater air pressure inside the bag, which inflates the bag.

- The kinetic energy of the moving air converts into greater air pressure inside the bag, which inflates the bag.

The basket of a wheelbarrow is located in between its wheel and its handles. How does this arrangement make it relatively easy for you to lift a heavy load in the basket? - The lever arm of your hands on the wheelbarrow handle is equal to the lever arm of the wheelbarrow pushing up on the load. - The lever arm of the load is short compared to the lever arm of you lifting, so the force you exert is magnified. - The force of your hands on the wheelbarrow handle is equal to the force of the wheelbarrow pushing up on the load. - The wheel of the wheelbarrow provides a mechanical advantage.

- The lever arm of the load is short compared to the lever arm of you lifting, so the force you exert is magnified.

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. - The hot patch would appear brighter than light from the surrounding skin. - The light from the hot patch would have a shorter wavelength than light from the surrounding skin. - The light from the hot patch would be brighter and have a longer wavelength than light from the surrounding skin.

- The light from the hot patch would be brighter and have a shorter wavelength than light from the surrounding skin.

If a motorcycle accelerates too rapidly, its front wheel will rise up off the pavement. During this stunt the pavement is exerting a forward frictional force on the rear wheel. How does that frictional force cause the front wheel to rise? - The frictional force causes a lifting force on the front tire. - The line of the frictional force passes beneath the center of mass, and so produces a backward torque. - The rear wheel accelerates forward faster than the front wheel, so the motorcycles rotates backward. - The frictional force causes the center of mass to rise.

- The line of the frictional force passes beneath the center of mass, and so produces a backward torque.

Some wind chimes consist of sets of metal rods that emit tones when they're struck by wind-driven clappers. These equal-diameter rods bend back and forth as harmonic oscillators. Why do the longer rods emit lower pitched tones than the shorter rods? - The longer rods have less mass and are less stiff than the shorter rods. - The longer rods have more mass and are less stiff than the shorter rods. - The longer rods have more mass and are stiffer than the shorter rods. - The longer rods have less mass and are stiffer than the shorter rods.

- The longer rods have more mass and are less stiff than the shorter rods.

Why do meats and vegetables cook much more quickly when there are metal skewers sticking through them? - The metal skewers create openings where the heat can get in. - The metal skewers conduct thermal energy to the interior of the food. - The skewers damage the food and make it more susceptible to being heated. - The metal skewers conduct heat to the interior of the food.

- The metal skewers conduct heat to the interior of the food.

Why are the tides relatively weak near the north and south poles? - The moon's gravity and the sun's gravity cancel one another at the north and south poles. - The moon's gravity produces one tidal bulge on the earth's oceans. That tidal bulge peaks near the equator on the side of the earth nearest the moon. - The moon's gravity produces two tidal bulges in the earth's oceans. Those tidal bulges peak near the equator, one on the side of the earth nearest the moon and one on the side of the earth farthest from the moon. - The moon's gravity causes the water level to rise and fall rhythmically in a uniform ring around the equator.

- The moon's gravity produces two tidal bulges in the earth's oceans. Those tidal bulges peak near the equator, one on the side of the earth nearest the moon and one on the side of the earth farthest from the moon.

Which does more work in lifting a grain of rice over its head: an ant or a person? - The answer depends on additional factors not mentioned here. - The ant does more work. - The person does more work. - Both do equal work.

- The person does more work.

How does the string of a yo-yo get the yo-yo spinning? - Friction between the string and the axle produces an unbalanced torque. - The force of the string pulling up produces an unbalanced torque on the yo-yo. - The point where the string touches the axle is the axis of rotation. - The weight of the yo-yo produces an unbalanced torque about this point. - The string force is less than the weight of the yo-yo, so the yo-yo accelerates downward.

- The point where the string touches the axle is the axis of rotation. - The weight of the yo-yo produces an unbalanced torque about this point.

If you drop a full can of applesauce and it strikes a cement floor squarely with its flat bottom, what happens to the pressures at the top and bottom of the can? - The pressure at the top is equal to the pressure at the bottom. - The pressure at the top is lower than the pressure at the bottom. - The pressure at the top is higher than the pressure at the bottom. - There is no particular relationship between the pressure at the top and at the bottom.

- The pressure at the top is lower than the pressure at the bottom.

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? - It is harder to pull air down to that depth. - The air pressure is greater at that depth. - The air in your lungs is at greater pressure. - The pressure due to the depth of the water above your chest presses in on you.

- The pressure due to the depth of the water above your chest presses in on you.

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 greater than that of the surrounding air. - The pressure in your lungs is less than that of the surrounding air. - The pressure in your lungs is equal to that of the surrounding air. - There is no specific relationship between the pressure in your lungs and the pressure of the surrounding air.

- The pressure in your lungs is less than that of the surrounding air.

Why does a relatively modest narrowing of the coronary arteries, the blood vessels supplying blood to the heart, cause a dramatic drop in the amount of blood flowing through them? - The rate at which blood flows is proportional to the diameter of the blood vessel to the third power. - The rate at which blood flows is inversely proportional to the diameter of the blood vessel. - The rate at which blood flows is proportional to the diameter of the blood vessel to the fourth power. - The rate at which blood flows is proportional to the diameter of the blood vessel squared.

- The rate at which blood flows is proportional to the diameter of the blood vessel to the fourth power.

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 transfers heat from outside itself to inside itself. - To remove energy from the room would require an air conditioner, not a refrigerator. - The refrigerator releases more energy as heat than it removes from the air inside itself. - The refrigerator does 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 flame radiates heat upward. - Cooler air comes in at the bottom. - The rising warm air causes the flame to elongate upward. - The warm air rises.

- The rising warm air causes the flame to elongate upward.

Explain why a rolling pin flattens a piecrust without encountering much sliding friction as it moves. - The flattening is caused by static friction between the rolling pin and the crust. - The flattening is caused by the weight of the rolling pin, not sliding friction. - Actually, there is a lot of sliding friction. That's what flattens the crust. - The rolling pin is pushing down on the crust, not sliding along it.

- The rolling pin is pushing down on the crust, not sliding along it.

Some racing cars are designed so that their massive engines are near their geometrical centers. Why does this design make it easier for these cars to turn quickly? - Putting the engine near the center makes it weigh less. - The rotational mass is smaller with this design, so a larger angular acceleration (quicker turn) is possible. - The weight of an engine near the center of mass will have a small lever arm about an axis through the center of mass. - The best spot for the engine is at the center of mass.

- The rotational mass is smaller with this design, so a larger angular acceleration (quicker turn) is possible.

Why is it so exhausting to run on soft sand? - The sand converts most of the energy of its collision with your feet into thermal energy instead of returning it to you. - The sand reduces the coefficient of restitution of your feet. - The sand has a low coefficient of restitution. - It takes more energy to run on sand.

- The sand converts most of the energy of its collision with your feet into thermal energy instead of returning it to you.

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? - It doesn't matter which side. - The black side. - The shiny side.

- The shiny side.

One way to crack open a walnut is to put it in the hinged side of a door and then begin to close the door. Why does a small force on the door produce a large force on the shell? - The large force on the shell is friction between the shell and the door. - The small force on the door has a large lever arm, but the force on the walnut has a small lever arm. - The force on the door has a small lever arm, but the force on the walnut has a large lever arm. - A small torque on the door produces a large torque on the walnut.

- The small force on the door has a large lever arm, but the force on the walnut has a small lever arm.

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. - The snow needs some time before it can start melting. - The warmth of the room takes a while to penetrate the snow. - The snow needs to come up to room temperature before it can start melting.

- The snow's temperature needs to rise to 0 °C before it can start melting.

A ball falls from rest for 5 seconds. Neglecting air resistance, during which of the 5 seconds does the ball's speed increase most? - The last second. - The first second. - The speed change is the same during each of the 5 seconds. - There is not enough information to determine the answer.

- The speed change is the same during each of the 5 seconds.

Bicycle racers sometimes wear teardrop-shaped helmets that taper away behind their heads. Why does having this smooth taper behind them reduce the drag forces they experience relative to those they would experience with more ballshaped helmets? - The teardrop shape is more streamlined and thus airflow around it is not laminar. The drag on it is mostly viscous drag. - The teardrop shape is more streamlined and thus has almost no turbulent wake. The drag on it is mostly pressure drag. - The teardrop shape is more streamlined and thus has almost no turbulent wake. The drag on it is mostly viscous drag. - The teardrop shape is more streamlined and thus airflow around it is not laminar. The drag on it is mostly pressure drag.

- The teardrop shape is more streamlined and thus has almost no turbulent wake. The drag on it is mostly viscous drag.

A toy top spins for a very long time on its sharp point. Why does it take so long for friction to slow the top's rotation? - Actually, it is air resistance which slows the top's rotation. - The top's point is very small, so the frictional force generated is small. - A heavy top will stop faster due to increased friction between the tip and the ground. - The top's point is very small, so the frictional torque generated is small.

- The top's point is very small, so the frictional torque generated is small.

How does a bottle opener use mechanical advantage to pry the top off a soda bottle? - The lever arm of your hand on the bottle opener is much smaller than the force on the bottle cap. - The lever arm of your hand on the bottle opener is equal to the lever arm of the bottle opener on the bottle cap. - The force of your hand on the bottle opener is equal to the force of the bottle opener on the bottle cap. - The torque of your hand on the bottle opener is equal to the torque of the bottle opener on the bottle cap.

- The torque of your hand on the bottle opener is equal to the torque of the bottle opener on the bottle cap.

When you turn while riding a bike, you must lean in the direction of a turn or risk falling over. If you lean left as you turn left, why don't you fall over to the left? - You don't fall over to the left because the momentum of the bike is to the left. - The torque produced by leaning left counterbalances the torque produced by the ground on the tires, so there is no net torque about the center of mass. - The torque produced by leaning left counterbalances the torque produced by the tires on the ground, so there is no net torque about the center of mass. - The torque produced by leaning left is what causes the bikes to rotate as it turns to the left.

- The torque produced by leaning left counterbalances the torque produced by the ground on the tires, so there is no net torque about the center of mass.

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 more dense than the lower liquid. - The liquids can be mixed if you shake the toy vigorously. - The upper liquid is less dense than the lower liquid. - The upper liquid is filled with air.

- The upper liquid is less dense than the lower liquid.

If you try to fill a bucket by holding it in a waterfall, you will find the bucket pushed downward with enormous force. How does the falling water exert such a huge downward force on the bucket? - The water has a lot of inertia. - The water goes from high speed and low pressure to low speed and high pressure when it hits the bucket. - The water has a lot of momentum. - The falling water pushes on the bucket.

- The water goes from high speed and low pressure to low speed and high pressure when it hits the bucket.

You are traveling in a subway along a straight, level track at a constant velocity. If you close your eyes, you can't tell which way you're heading. Why not? - The vibration of the subway car masks the sensation of motion. - You can't see where you're going. - You can't feel the wind inside a closed box. - There is no feeling of acceleration.

- There is no feeling of acceleration.

When an airplane starts its propellers, they spin slowly at first and gradually pick up speed. Why does it take so long for them to reach their full rotational speed? - They have a large rotational mass. - Air resistance slows it down. - They have a large mass. - Friction slows it down.

- They have a large rotational mass.

Frozen vegetables will "freeze-dry" if they're left in cold, dry air. How can water molecules leave the frozen vegetables? - They melt away. - They evaporate into the surrounding air. - They dissolve into the food. - They sublime into the surrounding air.

- They sublime into the surrounding air.

Racing bicycles often have smooth, disk-shaped covers over the spokes of their wheels. Why would these thin wire spokes be a problem for a fast-moving bicycle? - They would create turbulence and increase drag. - They would decrease the Reynolds number of the air flow. - They would increase the turbulent drag. - They would create more laminar flow.

- They would create turbulence and increase drag.

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. - Actually, this device violates the first law of thermodynamics, not the second law. - Perpetual motion machines can't exist. - It violates the law of thermal equilibrium. - This device would be decreasing the entropy of the universe.

- This device would be decreasing the entropy of the universe.

Why are the highest pitched strings on most instruments, including guitars, violins, and pianos, the most likely strings to break? - To vibrate at the highest pitches, these strings must be thin and short. That combination makes them prone to breaking. - To vibrate at the highest pitches, these strings must be thick and taut. That combination makes them prone to breaking. - To vibrate at the highest pitches, these strings must be thin and taut. That combination makes them prone to breaking. - To vibrate at the highest pitches, these strings must be thick and short. That combination makes them prone to breaking.

- To vibrate at the highest pitches, these strings must be thin and taut. That combination makes them prone to breaking.

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? - Actually you can, you just have to be very careful. - The brook with eddies and vortices has laminar flow. - Turbulent water flows in unpredictacle directions.

- Turbulent water flows in unpredictacle directions.

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. - Atmospheric pressure is lower in Denver than in New York. - It's colder at higher altitudes. - Boiling is harder at higher altitudes.

- Water has a lower boiling temperature in Denver than in New York.

Sprinters start their races from a crouched position with their bodies well forward of their feet. This position allows them to accelerate quickly without tipping over backward. Explain this effect in terms of torque and center of mass. - When the runner takes off there will be a large frictional force of the ground against their feet, which will produce a large torque rotating them forward. The fact that their center of mass is well forward of their feet means that there will be a counterbalancing torque rotating them backward, which will keep them from toppling. - When the runner takes off there will be a large frictional force of their feet against the ground, which will produce a large torque rotating them backward. The fact that their center of mass is well forward of their feet means that there will be a counterbalancing torque rotating them forward, which will keep them from toppling. - When the runner takes off there will be a large frictional force of the ground against their feet, which will produce a large torque rotating them backward. The fact that their center of mass is well forward of their feet means that there will be a counterbalancing torque rotating them forward, which will keep them from toppling. - When the runner takes off there will be a large frictional force of their feet against the ground, which will produce a large torque rotating them forward. The fact that their center of mass is well forward of their feet means that there will be a counterbalancing torque rotating them backward, which will keep them from toppling.

- When the runner takes off there will be a large frictional force of the ground against their feet, which will produce a large torque rotating them backward. The fact that their center of mass is well forward of their feet means that there will be a counterbalancing torque rotating them forward, which will keep them from toppling.

An electric valve controls the water for the lawn sprinklers in your backyard. Why do the pipes in your home shake whenever this valve suddenly stops the water but not when the valve suddenly starts the water? - Any shaking is absorbed by the flowing water. - The shaking is from the vibration of the valve slamming shut. - When the valve closes the water flow stops suddenly, resulting in a water hammer, but when the valve opens the flow does not instantly reach full speed. - The pipes do shake when the flow starts, but you're less likely to notice it.

- When the valve closes the water flow stops suddenly, resulting in a water hammer, but when the valve opens the flow does not instantly reach full speed.

When you climb out on a thin tree limb, there's a chance that the limb will break off near the trunk. Why is this disaster most likely to happen when you're as far out on the limb as possible? - When you are far out on the limb the lever arm of your weight (about an axis at the trunk) is large. - Bad things always happen at the worst possible time. - Your weight is greater the farther out you climb. - The limb is thinner and weaker the farther out you climb.

- When you are far out on the limb the lever arm of your weight (about an axis at the trunk) is large.

A barometer, which is often used to monitor the weather, is a device that measures air pressure. How could you use a barometer to measure your altitude as you climbed in the mountains? - You could tie a long string to the barometer, lower it to the ground below, then pull it back up and measure the string. - You could use a chart of altitude as a function of air pressure. - You could trade the barometer to another mountain climber in return for him telling you your altitude. - You could throw the barometer off the mountain measure its time of fall, and from that get your altitude.

- You could use a chart of altitude as a function of air pressure.

Your car is on a crowded highway with everyone heading south at about 100 km/h (62 mph). The car ahead of you slows down slightly and your car bumps into it gently. Why is the impact so gentle? - Your car bumper converts most of the energy of the collision into thermal energy. - You speed in approaching the other car is very small. - Your car bumper has a high coefficient of restitution. - The other car rebounds off your bumper with most of the collision energy.

- You speed in approaching the other car is very small.

You are walking with a full cup of coffee in your hand and it begins to slosh wildly in the cup. When you start walking slightly faster, the sloshing motion nearly vanishes. Why was the sloshing strongest when you were walking at the slower pace? - The coffee needs more total energy to travel faster, so it converts the energy from its sloshing motion into its overall kinetic energy. - You have more energy when you are traveling faster. - Your steps were synchronized to the sloshing motion and you were transferring energy to the coffee's sloshing motion via resonant energy transfer. - You have less energy when you are traveling faster.

- Your steps were synchronized to the sloshing motion and you were transferring energy to the coffee's sloshing motion via resonant energy transfer.

Two teams are having a tug-of-war with a sturdy rope. It has been an even match so far, with neither team moving. What is the net force on the left team? - Both toward and away from the right team - Away from the right team - Zero - Toward the right team

- Zero

The back of your car seat has a head rest to protect your neck during a collision. The type of collision which causes your head to press against the headrest is - a rear-end collision. - a side-impact collision. - a head-on collision. - none of these.

- a head-on collision.

The kicker in a sporting event isn't always concerned with how far downfield the ball travels. Sometimes the ball's flight time is more important. If he wants to keep the ball in the air as long as possible, he should kick it - at a large angle from the ground. - at a 45° angle. - with a lot of spin. - low to the ground.

- at a large angle from the ground.

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 - that is left over when it converts thermal energy from the inside air into electricity. - it produces during its defrost cycle; when it warms up its evaporator to remove ice that forms because of the humidity. - it removes from the inside air and the heat it produces from the electricity it consumes. - it produces from the electricity it consumes.

- it removes from the inside air and the heat it produces from the electricity it consumes.

The chairs in an auditorium aren't all facing the same direction. How could you describe their angular position in terms of a reference orientation and a rotation? - meters south of the north wall and east of the west wall - radians from the north wall - radians clockwise from north - meters clockwise from north

- radians clockwise from north

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 - at the same rate as on earth, but with a smaller swing. - at the same rate as on earth, but with a larger swing. - faster than on earth. - slower than on earth.

- slower than on earth.

An unseatbelted driver can be injured by the steering wheel during a head-on collision. The driver hits the steering wheel when the car suddenly comes to a stop because - the steering wheel is pushed back into the driver's head. - the force of the collision pushes the driver's head into the steering wheel. - gravity makes the head move forward. - the driver's head has inertia.

- the driver's head has inertia.

When you begin to walk forward, the force that allows you to accelerate is - the friction force of the ground exerted on your feet. - the ground pushing up on your feet. - the friction force of your feet exerted on the ground. - the weight of your feet on exerted on the ground.

- the friction force of the ground exerted on your feet.

As you begin pedaling your bicycle and it accelerates forward, the forward force that the bicycle needs to accelerate is exerted by - your feet on the pedals. - the ground on the tires. - the tires on the ground. - the pedals on your feet.

- the ground on the tires.

A blacksmith usually hammers hot metal on the surface of a massive steel anvil. The reason this is more effective than hammering the hot metal on the surface of a thin steel plate is - the massive anvil can absorb more heat than a thin steel plate. - the massive anvil has more inertia. - the anvil exerts more force on the hot metal.

- the massive anvil has more inertia.

If you pull slowly on the top sheet of a pad of paper, the whole pad will move. But if you yank suddenly on the sheet, it will tear away from the pad. The reason for these different behaviors is - the sudden pull isn't strong enough to make the pad move. - the pad has inertia. - gravity holds the pad in place during the sudden pull. - the slow pull is a stronger force.

- the pad has inertia.

Stamping your feet cleans the snow off of them because - the heat generated by the stamping melts the snow somewhat. - the vibration of the stamping lowers the friction between the snow and the foot. - the snow on your feet has inertia. - the force of the stamping knocks it off.

- the snow on your feet has inertia.

Putting sand in the trunk of a car helps to keep the rear wheels from skidding on an icy road because - the sand can shift around a bit and distribute its weight in the trunk more evenly. - the weight of the sand makes the wheels and the road press together harder. - the gritty sand increases the traction between the wheels and the road. - it makes the car weigh more.

- the weight of the sand makes the wheels and the road press together harder.

Loose objects on the dashboard slide to the right when the car turns suddenly to the left because - inertia pushes the loose objects to the right. - gravity isn't strong enough to hold them in place. - there is a force to the right. - they have inertia.

- they have inertia.

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. - both forward and backward. - in the backward direction. - in the forward direction.

- zero.