MIDTERM 2
Your friends have purchased an old house that has significant mineral accumulation inside its pipes. Every pipe in the house is now effectively half the diameter it was when new. For example, a pipe that had a 1-inch diameter opening when new now has a 0.5-inch diameter opening. If it took 10 minutes to fill the bathtub when the house was new, how long does it now take to fill the bathtub?
160 mins
To win a prize at the fair, you must tip over a heavy jug by hitting it with a 1-kg object. Your best bet is to transfer as much momentum as possible to the jug, so which of the following 1-kg objects should you throw at the jug?
Answer: (A) An object of medium hardness that is bounces very well.
A birdfeeder hangs motionless from a tree branch on a long string. After a bird disturbs it, the birdfeeder swings back and forth below the branch before settling back to its original stable equilibrium position. Why is the birdfeeder's equilibrium position stable?
Answer: (A) Since the birdfeeder's total potential energy always increases whenever it is displaced from its equilibrium, it tends to accelerate back toward that equilibrium
You drop an unopened metal can of soup and it lands bottom-first on the floor. When you inspect the can, you see that has dented outward in places. Where did it dent outward and why?
Answer: (A) The soup pressure near the bottom of the can increased dramatically as the soup transferred its momentum suddenly to the floor and that pressure dented the can outward near its bottom.
Two coins slide horizontally off a tabletop side-by-side at the same instant and begin to fall. The US quarter was moving twice as fast as the US dime when the two coins left the tabletop. Where and when do the coins hit the level floor beneath the table? [neglect any effects due to the air.
Answer: (A) The two coins hit the ground at the same time, but the quarter lands about twice as far from the table as does the dime. [96.7% picked]
A pressure washer is used to clean stone surfaces. Its pump delivers high-pressure water to a hose and that water is sprayed through a nozzle so this travels through the air and hits the stone surface. Which of the following correctly describes the water's pressure?
Answer: (A) The water's pressure is high before the nozzle, it is atmospheric pressure as it travels through the air, and it is high when it is slowed down by the stone surface. [74.8% picked]
Two shiny plastic balloons are identical in every way except that one contains air and the other contains helium. Which one of the following statements about the two balloons is true?
Answer: (A) They have the same particle density, different densities, and different weights.
Firefighters are battling a fire on the 10th floor of a building. Their truck draws water from a fire hydrant, pressurizes it with a pump, and delivers it to a hose with a nozzle. When sprayed upward from ground level, the water only reaches the 8th floor. To get the water to reach the fire, what must the firefighters do? [Ignore viscosity and assume the water is in steady state flow after the pump.]
Answer: (A) Use a second pump to increase the pressure of water entering their hose. [88.6% pi
To avoid tipping over while turning right on a bicycle, why must you lean the bicycle toward your right?
Answer: (A) You accelerate rightward as you turn right and your inertia tends to make you tip over toward your left. By leaning toward your right, you cancel that tendency and avoid tipping over. [62.0% picked]
You are on a 10th floor hotel balcony, overlooking the pool. You lower a 100-foot-long straw into the pitcher of lemonade at the bar and try to suck the lemonade up to your mouth. What happens?
Answer: (A) You are unable to suck the lemonade up to your mouth.
You hold an ordinary helium-filled rubber balloon motionless in a small room filled with helium gas and then release the balloon. That balloon
Answer: (A) descends to the floor.
Water is flowing through a horizontal pipe in laminar, steady-state flow. Halfway along the pipe, its diameter decreases and the water must continue on through that narrow second half. Compared to when it was in the wide first half of the pipe, water in the narrow second half of the pipe is moving
Answer: (A) faster and its pressure is smaller. [61.2
Some fire extinguishers use spray carbon dioxide. The mass of a carbon dioxide molecule is about 50% greater than the mass of an average air molecule. At room temperature, a liter of carbon dioxide
Answer: (A) has the same number of particles as a liter of air, but the carbon dioxide weighs more than the air it displaces and it sinks to the floor.
You are paddling yourself forward in a Kayak, across a calm lake. Each time you pull the paddle backward through the water, from the front of the boat to its rear, the water exerts a force on the paddle that is
Answer: (A) in the forward direction, toward the front of boat.
When air is flowing past a ball, the most difficult part of its passage is from the middle of the ball to the back of the ball. During that part of the air's journey, the air pressure along each streamline
Answer: (A) increases and the airflow slows down.
You partially fill a rigid plastic container with hot soup, seal the container with a lid, and put the container in the refrigerator. Along with the soup, you trapped hot air in the rigid container. When you open the lid of the cold container, a few hours later, air rushes
Answer: (A) into the container. As the hot air you trapped in the rigid container cooled, its pressure decreased to less than atmospheric pressure.
You are standing in a slow-moving stream, facing upstream so that the water is coming toward the front of your body. You are wearing shorts and the water level is slightly above your bare knees. The water experiences perfect laminar flow around each of your nearly cylindrical legs. You measure the water pressure at a specific altitude below your right knee and find that the water pressure is
Answer: (A) largest on the front and back of your leg and smallest on the sides of your leg. [60.5% picked]
You are standing 10 feet north of a campfire in a level, open field. Despite the cool air all around you, you feel warmed by the fire. Heat is flowing from the fire to you
Answer: (A) mostly via thermal radiation.
A pitcher throws a curveball. While the spinning baseball is in the air between the pitcher and home plate, the forces acting on the ball are its weight, a buoyant force, drag forces, a lift force, and
Answer: (A) no other force
You are playing miniature golf with friends and, as part of one hole, your golf ball rolls on a series of different ramps. All of the ramps have flat surfaces, but some ramps are steeper than others. The steeper the ramp on which the ball rolls,
Answer: (A) the greater the ball's acceleration.
A hydrogen-filled dirigible (a huge blimp or elongated balloon) floats in air because the hydrogen-filled dirigible contains
Answer: (A) the same number of particles as the air it displaces, but each hydrogen molecule weighs less than the average air molecule.
Two toy cars roll off a level table side-by-side at the same time and in the same direction. The cars soon hit the level floor below the table. The orange car weighs twice as much as the green car, but both cars were traveling at the same horizontal speed when they left the table. In this situation,
Answer: (A) the two cars hit the floor at approximately the same time and the same distance from the table.
You are at an amusement park and are about to try the drop tower. It lifts you high in the air and then lets you fall freely for about 2 seconds. As you fall, your apparent weight is zero and you feel weightless because
Answer: (A) you experience an upward feeling of acceleration that exactly cancels your feeling of weight. [73.0% picked]
The exposed air ducts in warehouses and gymnasiums are often several feet in diameter. If a wide duct and a narrow duct are delivering the same amount of air each second, the fan pushing air through the wide duct consumes less power than the fan pushing air through the narrow duct. Why?
Answer: (B) Air in the wide duct moves slower, requiring less kinetic energy per liter, and it experiences weaker viscous interactions with the duct.
You inflate a rubber balloon with oxygen and then release it. The balloon flies around the room until it is empty and deflated. What pushed the balloon forward
Answer: (B) As the balloon pushed oxygen backward out of the balloon's opening that oxygen pushed the balloon forward. [90.4% picked]
At a baseball game, a pitcher throws a fastball toward the catcher. When the ball is half way to home plate and no one is touching it, where on the ball is the air pressure highest?
Answer: (B) At the front of the ball—the side nearest home plate.
A kicked soccer ball that is not spinning moves forward through air that had been motionless. Just after the ball has passed by, in which direction is the air's average velocity?
Answer: (B) Forward—in the direction of the ball's velocity.
After heavy rains, the water flowing down a nearby river is turbulent, also known as "white water." During a drought, however, the water flowing down that same river is laminar; it appears smooth and clear. Explain the difference.
Answer: (B) In the fast-moving water after the rains, inertia dominates the flow. In the slow-moving water during the drought, viscosity dominates the flow. [84.9% picked]
You remove a plastic container and its lid from the hot dishwasher. After snapping the lid on the container, you put the sealed container of air on the counter to cool. When you examine the container later, you find that its lid has bowed inward significantly, reducing the container's volume. How has the cooling process affected the air pressure and air density in the container?
Answer: (B) The air's pressure has decreased and its density has increased. [4
An enormous asteroid is coasting straight toward your space station. With impact exactly 100 hours away, you use a tiny missile to blow the asteroid into two equal pieces. The space station is saved! Neglecting gravity and the tiny momentum of the tiny missile, what happens to the asteroid's total momentum and center of mass after the missile explosion?
Answer: (B) The asteroid's total momentum remains unchanged after the explosion and its center of mass passes through the space station exactly 100 hours later. [54.8% picked]
Water is flowing through a hose that is lying on a slippery surface. Most of the hose is straight, but it bends 90° to the right just before its open end (see figure). You increase the water flowing through the hose and the bent portion of the hose begins to slide to the left (opposite the end). What pushes this portion of the hose toward the left?
Answer: (B) The increased water pressure inside the outer edge of the bend.
You are pulling a wagon full of children up a hill at constant velocity. Which one of the following statements is true?
Answer: (B) The net force on the wagon is zero and you are doing work on the wagon. [6
Suppose a rocket is launched vertically, so that its velocity always points vertically upward. By the time the rocket's fuel runs out, its altitude is 200 miles above the Earth's surface and its speed is approximately zero. What happens to the rocket after its fuel runs out?
Answer: (B) The rocket falls, accelerating vertically downward because of its weight. [65.1% picked]
You drop an unopened metal can of soup and it lands bottom-first on the floor. When you inspect the can, you see that it has dented outward in places. Where did it dent outward and why?
Answer: (B) The soup pressure near the bottom of the can increased dramatically as the soup transferred its momentum suddenly to the floor and that pressure dented the can outward near its bottom. [78.9% picked]
Water distribution systems often include water towers that are located well above all the rest of the plumbing. In addition to storing water, what is the purpose of the water tower?
Answer: (B) The tower also stores energy. [53.6% picked]
You are riding a train that is moving straight ahead at high speed. The train comes to a curve in the tracks and begins to turn toward the left. You find yourself pressed against the right side of your seat. What force, if any, is pushing you toward the right?
Answer: (B) There is no force pushing you toward the right.
You are moving a bucket of water around in a horizontal circle at a steady speed and the bucket remains 4 feet above the ground. A friend looking down on you from a balcony sees the bucket moving counter-clockwise around you: it is north of you, west of you, south of you, east of you, north of you, and so on. Just as the bucket reaches the point exactly north of you, you let go of the bucket. In which direction does the bucket travel after you release it?
Answer: (B) Toward the west
You are on a 3rd floor hotel balcony, 10 meters above the bar. You lower a long straw into a pitcher of diet soda (essentially pure water) and find that you can just barely suck the soda up to your mouth. You move the straw over to pitcher filled with full-calorie soda (essentially sugar water, with a density that is 10% more than pure water). Now what happens when you begin sucking?
Answer: (B) You are unable to suck the full-calorie soda up to your mouth.
On a hot afternoon, you seal your empty plastic water bottle and thus trap the hot air inside it. Later in the day, the bottle and its contents are much cooler and the elastic sides of the bottle are now bent inward. The bottle's volume has decreased. Based on these changes, you can be certain that the air pressure inside the bottle has
Answer: (B) decreased and the density inside the bottle has increased.
On a hot afternoon, you seal your empty plastic water bottle and thus trap the hot air inside it. Later in the day, the bottle and its contents are much cooler and the elastic sides of the bottle are now bent inward. The bottle's volume has decreased. Based on these changes, you can be certain that the air pressure inside the bottle has
Answer: (B) decreased and the density inside the bottle has increased. [
A simple squirt gun is a hand-operated toy that shoots a stream of water. As your finger pushes on a moving part of the gun, water emerges from the gun's nozzle and shoots straight upward. As you push harder on the gun's moving part, the stream of water goes higher because you are
Answer: (B) doing more work on each drop of water flowing through the gun and each drop thus has more total energy to turn into gravitational potential energy as it rises.
A 10-inch diameter wooden ball is floating on a calm fresh-water lake at sea level. The top of the ball is exactly 1 inch above the level of the water. When you transfer that ball to a fresh-water lake high up in the mountains, the ball
Answer: (B) floats deeper in the water, so that its top is less than 1 inch above the level of the water. [75.3% picked]
You are jogging northward along the ocean on a calm, windless day and are experiencing a pressure drag force that pushes you southward. A viewed by someone standing motionless on the beach, the average velocity of the air a few inches (a few centimeters) behind you is
Answer: (B) greater than zero and directed northward. [81.5% picked]
You are driving forward in a sports car with the windows closed. A squirrel runs across the road and you slam on the brakes. As the car slows to a stop, missing the squirrel, the air pressure inside the car is
Answer: (B) higher near the front of the car than near the back of the car. [89.5%
The maximum speed of a rocket-propelled spaceship with an exhaust speed of 5000 mph is
Answer: (B) limited only by the ratio of fuel to spaceship.
If a golf ball had no dimples and were smooth instead, it would
Answer: (B) lose forward momentum more quickly and travel less far.
Water hammer occurs when you suddenly stop the rapid flow of water in a pipe and results in the pipe-end experience a huge force in the direction of the water's original motion. It happens because flowing water has
Answer: (B) momentum.
An airplane cruises forward at constant velocity through a region of calm, motionless air. After the plane has passed through that region of air, the air's total momentum is
Answer: (B) nonzero and directed exactly downward.
A gymnasium has a large ventilation duct near its ceiling. When air that was moving at uniform velocity and pressure through a straight section of duct enters a bend in the duct and it curves, its pressure is greatest at the [neglect any effects due to viscosity or turbulence]
Answer: (B) outside of the bend and its speed is greatest at the inside of the bend. [90
The dry cleaner returns your cloths protected by large, very thin plastic bags. You seal two of these bags with tape and fill one bag with air and the other bag with natural gas (methane). You inflate them until they are full but not taut (the plastic is still limp). The bags are identical in every way except for the difference in gas (air versus methane). When you let go of the two bags, the air-filled bag descends and the methane-filled bag rises. The bags have equal
Answer: (B) particle densities (number of gas particles per cubic meter), but the methane-filled bag weighs less than the air-filled bag.
As a soccer ball travels from the kicker to the goal, air approaches the front of the ball and they interact. The ball loses much of its forward momentum during its flight because
Answer: (B) the air at the front of the ball is higher than atmospheric pressure while the air behind the ball is approximately atmospheric pressure.
You are floating along in a hot air balloon. You look up and notice that the bottom of the balloon is open. Apart from a few molecules that diffuse out, hot air remains inside the balloon despite this opening because
Answer: (B) the air pressure just inside the opening is the same as the air pressure just outside that opening.
You're filming a movie and you arrange for two unoccupied cars to drive horizontally off a tall cliff side-by-side at the same velocity. The Mercedes sedan weighs twice as much as the Mini Cooper. In this situation, the two cars hit the level ground below the cliff at approximately
Answer: (B) the same time and at the same distance from the cliff.
As water in steady state flows straight up in a vertical pipe with a uniform diameter, that water
Answer: (B) transforms its pressure potential energy into gravitational potential energy. [79.1% picked]
If you drop a penny off the Empire State Building, it will accelerate for only about 2 seconds and then coast all the way to the sidewalk at a constant terminal velocity of about 25 miles per hour downward. The penny is evidently experiencing an upward force that is equal in amount to the penny's weight. What force is pushing the penny upward?
Answer: (C) A pressure drag force (there is a turbulent wake above the penny).
You roll a baseball off the top of a tall building and it hits the ground 4 seconds later. When the baseball has fallen for only 2 seconds, how far is it above the ground?
Answer: (C) It is 3/4 of the building's height above the ground.
A baseball pitcher throws the baseball so that it spins rapidly as it moves toward the catcher. The ball's top surface is spinning toward the pitcher and its bottom surface is spinning toward the catcher. What vertical force(s) is the ball experiencing as it travels through the air?
Answer: (C) Its weight downward, a lift force upward, and a buoyant force upward.
A wooden ball floats motionless on the water in a large bowl. Only half of the ball is in the water. You pour some salad oil into the bowl and that oil floats on the surface of the water. What fraction of the ball is in the water now?
Answer: (C) Less than half of the ball is in the water.
An airplane is cruising horizontally at 30,000 feet and maintains constant velocity. How does the airplane avoid falling?
Answer: (C) The airplane pushes downward on the passing airstream with a force equal to the airplane's weight and the airstream exerts an equal but opposite force upward on the airplane. [86.7% picked]
A log is floating motionless on a calm lake, with about half the log located beneath the water level. It's a sunny day and the temperature of the air increases, although the air pressure remains constant. How does the air's increasing temperature affect the log?
Answer: (C) The log descends slightly, so that more of it is located beneath the water level.
A player kicks a soccer ball directly toward the goal. As the ball moves through the air, what part(s) of the ball experiences the greatest air pressure?
Answer: (C) The part of the ball closest to the goal experiences the greatest air pressure. [83.3% picked]
Doctors use a centrifuge to separate red blood cells from blood plasma. The centrifuge swings a container of blood at high speed in a circular path. The red bloods drift away from the center of the circle, leaving the blood plasma nearer the center. Describe the pressures and densities in the blood as the centrifuge swings it in a circle.
Answer: (C) The pressure is highest farthest from the center of the circle and the red blood cells are denser than the blood plasma. [
Your friend is a famous sculptor and she has just completed the first sculpture in a series called "Stand Up Straight." Alas, whenever she sets the sculpture upright on the horizontal concrete floor and lets go of it, the sculpture tips over. Why won't this sculpture remain upright?
Answer: (C) The sculpture can decrease its total potential energy by tipping
You drop an unopened metal can of soup and it lands bottom-first on the floor. When you inspect the can, you see that it has dented outward in places. Where did it dent outward and why?
Answer: (C) The soup pressure near the bottom of the can increased dramatically as the soup transferred its momentum suddenly to the floor and that pressure dented the can outward near its bottom.
You kick a soccer ball through the air. From the ball's perspective, air is flowing northward toward the ball. Describe the air pressures on the ball's south side and east side (see figure).
Answer: (C) The south side pressure is greater than atmospheric pressure. The east side pressure is less than atmospheric pressure.
A carbon dioxide molecule has more mass than the average air molecule. You blow two large soap bubbles, one filled with ordinary air and one filled with carbon dioxide. The bubbles look identical and they are both at room temperature. How do the bubbles compare?
Answer: (C) They contain the same number of gas particles, their pressures are equal, and they experience the same buoyant force, but the carbon dioxide bubble weighs more than the air bubble.
A horizontal pipe bends toward the right. As water flows steadily through this pipe, what happens as the water starts to travel around the bend?
Answer: (C) Water near the inside of the bend speeds up and water near the outside of the bend slows down. [83.5% picked]
You are driving Northward on a highway when you come to a smooth 90° turn toward the right. You maintain a constant speed around the turn and are soon driving Eastward. During the middle of the turn, in which direction were you accelerating?
Answer: (C) You were accelerating toward the Southeast.
You're filming a movie and you arrange for two unoccupied cars to drive horizontally off a tall cliff. The Mercedes sedan weighs twice as much as the Mini Cooper, but the Mini Cooper is traveling at twice the velocity of the Mercedes when the two cars careen off the cliff side-by-side. In this situation, the two cars hit the level ground below the cliff
Answer: (C) at approximately the same time, but the Mini Cooper hits considerably farther from the cliff than the Mercedes sedan. [86.9% picked]
A tennis player hits the tennis ball forward with "topspin," meaning that the top of the ball is moving forward relative to the rest of the ball. This spinning ball experiences a strong downward lift force and bends downward toward the ground after going over the net. One reason why this ball is experiencing that aerodynamic lift force is that the ball's spin
Answer: (C) causes the air to flow faster and farther around the bottom of the ball than around the top of the ball. [43.3% picked]
You are riding a roller coaster and your speed is increasing as you plunge downhill on the first hill. Your acceleration is directed
Answer: (C) downhill, your feeling of acceleration is directed uphill, and your apparent weight is smaller in amount than your actual weight. [49.3% picked]
The roller coaster you are riding is going through a loop-the-loop at high-speed. At the moment when you are at the top of the loop, you and your car are inverted yet you feel an apparent weight directed toward the sky. At this moment, your acceleration is
Answer: (C) downward and greater than the acceleration due to gravity. [8
A wooden ball floats motionless in a glass of water so that exactly half the ball is beneath the water's surface. Salad oil is about 10% less dense than water. If you place the same wooden ball in salad oil, the ball will
Answer: (C) float motionless with more than half the ball beneath the oil's surface. [72.
Water is flowing gently out of the end of a garden hose. You block off most of the hose's opening with your thumb and now the water sprays out at high speed because you
Answer: (C) have reduced the water's speed in the hose so that it wastes less of its ordered energy. [56.7% picked]
You are cleaning a wall by spraying water at it from a hose. At the center of the stream of water, right where it hits the wall, the water is coming to a complete stop. If you were to measure the water pressure at that point, you would find that it is
Answer: (C) higher than atmospheric pressure.
You kick a soccer ball so that it curves toward your left as it travels toward the goal. The ball curves toward your left because
Answer: (C) it is deflecting the airflow around it toward your right. [83.3% picked]
As water flows downward in a vertical pipe that has a uniform diameter, the water's gravitational potential energy decreases,
Answer: (C) its pressure potential energy increases, but its kinetic energy remains constant. [84.1% picked]
A block of wood floats motionless on a calm lake. Part of the block is in water and part of it is in air. As the day becomes hotter and the density of the air decreases, the block of wood
Answer: (C) moves downward so that more of the block is in water and less of the block is in air. [82.8% picked]
If a golf ball were smooth rather than dimpled, it would
Answer: (C) not travel as far after being hit by a golf club.
You are trying to increase the pressure in your village's water distribution system by modifying the local water tower. You should make that water tower
Answer: (C) taller (increase its altitude).
You are bicycling at constant velocity along a horizontal road and you are wearing a backpack. As you bicycle, you are doing
Answer: (C) zero work on the backpack and it is doing zero work on you. [
You are trying to set the world's record for drinking water through the tallest drinking straw. What could you do to have the best chance of setting this record?
Answer: (D) Go to the lowest altitude available, preferably sea level or below. [
You are working in a pizza parlor. You toss a spinning disk of pizza dough into the air. As the dough stretches outward and the flying disk becomes wider, what happens to the disk's angular velocity?
Answer: (D) It decreases.
You heat your metal water bottle on a stovetop until it is filled with hot air at atmospheric pressure. You then seal the bottle and set it on the kitchen counter to cool. Assume the bottle doesn't change size (volume) throughout this process. During the cooling process, what happens to the density and pressure of the air in the bottle?
Answer: (D) The density remains constant, but the pressure decreases.
Water is flowing at constant velocity through a straight horizontal pipe. It is experiencing two forces: a forward force due to a difference in pressure at the two ends of the pipe and a backward force due to the water's viscosity and friction with the stationary pipe. How do the amounts of those two forces compare?
Answer: (D) The two forces are equal in amount.
Firefighters are battling a fire on the 10th floor of an apartment building. When they stand on the ground, their fire hose can only shoot the water steadily up to the 8th floor. So they carry the nozzle end of the same fire hose to the top of a 4-story-tall ladder and again point the nozzle upward. How does the speed of the water as it emerges from the nozzle near the top of the ladder compare to its speed when it emerged from the nozzle near the ground?
Answer: (D) The water emerging from the nozzle near the top of the ladder travels more slowly. [65.8% picked]
You and your friend are riding a carousel. Your horses are side-by-side and your friend is closer to the center of the carousel than you are. As the carousel turns steadily, which of the following is true?
Answer: (D) You experience a larger inward acceleration than your friend does.
You are an astronaut spacewalking independently near your ship when you discover that your suit's propulsion system has failed. You and the ship are both coasting forward and are maintaining a constant separation of 100 feet (30 meters). There is danger in the distance, so you need to get to your ship. Fortunately, you have a hammer in your hand. To get to your ship, you throw the hammer
Answer: (D) away from the ship (in the direction that points from the ship to you).
When water flows around a bend in a garden hose, the water pressure
Answer: (D) decreases near the inside of the curve and increases near the outside of the curve. [95.1% picked]
You want to help a seriously ill person, but the door to their room is locked. To have the best chance of breaking the door open, you run toward the door (to accumulate forward momentum) and then hit the door with your
Answer: (D) hard feet and jump strongly so that you end up moving backward at the same speed you had before hitting the door.
You are cleaning your car with water from a hose and nozzle. At the center of the stream of water, right where it hits the side of your car, the water is almost coming to a complete stop and its water pressure is
Answer: (D) higher than atmospheric pressure.
You are cleaning your car with water from a hose and nozzle. At the center of the stream of water, right where it hits the side of your car, the water is almost coming to a complete stop. The pressure in the water at the center of the stream as it touches the car is
Answer: (D) higher than atmospheric pressure.
On a cold morning, you seal your empty plastic water bottle and thus trap the air inside it. Later in the day, the bottle and its contents are much warmer and the sides of the bottle are now bowed outward. As a result of these changes, the air pressure inside the bottle has
Answer: (D) increased and the density inside the bottle has decreased. [88.3% picked
If the airflow passing over the top of an airplane wing suddenly breaks away from the surface of the wing and forms a turbulent wake, the airplane will experience a rise in
Answer: (D) pressure drag and a decrease in lift.
You are a stunt driver for a movie. Your car is motionless at the start of your stunt and both your actual weight and your apparent weight (your feeling of weight) are normal. You then drive your car at 100 mph up a ramp, over a wide river, and down a second ramp on the far side the river. While you are midway between the two ramps, your weight is [neglect any effects due to the air]
Answer: (D) still normal, but your apparent weight is zero.
An airplane is cruising horizontally at 30,000 feet and is traveling at constant velocity. The overall force that airplane exerts on the air points
Answer: (D) straight downward.
An apple sits motionless on a table. The amount of momentum that apple is transferring to the table each second is
Answer: (D) the apple's weight times 1 second.
You are at a barbeque and the bottle of hot sauce is almost empty. You put the cap on the bottle and swing it rapidly in a circle with its cap end pointing outward. The remaining sauce collects just inside the cap and you are able to extract enough to spice up your vanilla ice cream. This technique works because
Answer: (D) the bottle's rapid inward acceleration leaves the hot sauce behind so that it drifts toward the cap end of the bottle. [88.6% picked]
When you pull a tablecloth out from under a set of dishes, it's important to pull the cloth as fast as possible because
Answer: (D) the momentum transferred to the dishes is proportional to the time during which the cloth pulls on them.
A building with two floors has simple plumbing with no moving parts. If you try the showers on each floor, you will find that [neglect any effects due to viscosity or turbulence]
Answer: (D) the ordered energy per drop is the same on both floors, however, the upper floor has less pressure before the shower head and slower moving water after the shower head. [87.6% picked]
You are inflating a shiny plastic balloon with helium. The balloon starts as a thin, flat bag but it gradually gets thicker and rounder as it fills. At first, the thin plastic balloon doesn't float. But as you keep adding helium to the balloon and it gets thicker and rounder, it eventually begins floating because
Answer: (D) the weight of the helium-filled balloon increases as it fills, but the buoyant force it experiences increases much faster and eventually the buoyant force exceeds the balloon's weight.
Waterproof watches have a maximum depth to which they can safely be taken while swimming. Why?
Deeper than that depth the water pressure is so great it might damage the watch.
A spacecraft is moving eastward in a circular orbit 200 miles above the Earth's equator. It is time for the spacecraft to return to the ground. The most effective way to cause the spacecraft to begin descending toward the Earth's surface is to fire its rocket engine. In which direction should the engine direct its rocket exhaust
Eastward
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.
Some clear toys contain two colored liquids. No matter how you tilt one of those toys, one liquid remains above the other. What keeps the upper liquid above the lower liquid
The upper liquid is less dense than the lower liquid.
You are pulling a wagon forward on a level sidewalk and the wagon is experiencing no other horizontal force. As you exert your forward force on the wagon, the wagon exerts a backward force on you. When do those two forces cancel so that the wagon does not accelerate?
They never cancel because they act on different objects.
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 use a chart of altitude as a function of air pressure.
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?
he gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.
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?
he pressure due to the depth of the water above your chest presses in on you.
A satellite is traveling around the earth in a circular orbit. It briefly fires its rocket engine to increase its speed in the forward direction; it is suddenly going faster but its direction of travel didn't change. As a result of this speed increase, the orbiting satellite's average distance from the center of the earth
increases.
You are competing in the 400-meter sprint on an oval track. As you round the final turn at world record pace, your path is curving toward your left and you find yourself leaning toward the left. Why can't you complete the turn safely if you don't lean and instead try to remain upright during the turn?
nswer: (A) Your feet will accelerate toward your left while your body coasts straight forward and you will tip over. [37.8% picked]
The chemical bond that causes two oxygen atoms to cling together as an oxygen molecules is
nswer: (A) a deficit of energy—the work needed to separate those two atoms from one another. [43.4% picked]
When you catch a ball that was thrown to you by a teammate, that ball exerts a force on your hand. Can the force that the ball exerts on your hand be larger than the force your teammate exerted on the ball when throwing it?
yes
