GSCI FINAL
You are swinging a tin can around your head in a perfectly horizontal circle and its acceleration is 32 m/s2. If its speed is 4 m/s what is the value of the radius of its circular path?
0.5 m
A ball hits a wall going 10 m/s, and bounces off going 7 m/s. The coefficient of restitution is
0.70 COR=bounce off speed/hit speed
Water settles to the bottom of a tank of gasoline. Which takes up more space: 1 kg of water or 1 kg of gasoline?
1 kg of gasoline because gasoline is less dense than water.
Atmospheric pressure is about 100000 Pa. At what depth in water does this pressure double?
10 m
If you double the absolute temperature of a star, its power output increases by a factor of
16
A bat moving at 90 km/h strikes an oncoming ball moving at 110 km/h. If the batter follows through so that the speed of the bat doesn't change during the hit and the coefficient of restitution of the ball is 0.6, what speed does the batted ball have after it has been struck?
210 km/h
You are a deep sea diver and are carrying out pressure test son your air tanks, which is required by inspection rules. A gas cylinder is filled with a gas at a temperature of 300 K and pressure 200000 Pa. The temperature of the gas is then raised to 400 K. What is the new pressure?
266667
Water weighs about 10 N per liter. A 4.0 liter ball is pushed underwater. What is the buoyant force on the ball?
40 N
If the water pressure at a pump station at sea level 4,000,000 Pa, how high can the water be pumped uphill, and how fast will it flow out of a faucet at a washing station at sea level?
408 m; 45 m/s
The coefficient of restitution for a particular ball is 0.45. If he ball hits a surface traveling at 100 m/s its rebound speed will be
45 m/s
The diameter of a pipe is tripled while the pressure difference across the pipe remains the same. The volume flow rate of the pipe increases by a factor of
81
The coefficient of restitution for a particular ball is 0.7. If he ball rebounds from surface traveling at 60 m/s its collision speed was
85.7 m/s
You are swinging a tin can around your head in a perfectly horizontal circle of radius 4 m. (This is really not possible but we're saying it almost happens.) If the speed of the can is 4 m/s and its mass is 2 kg, what inward force is required to keep the can moving in the circle?
8N
Tennis ball A is dry and fuzzy. Tennis ball B is wet, and the fuzz is matted down. What will happen when the two balls are hit horizontally so as to have the same initial horizontal velocity?
A goes farther than B because the fuzz reduces drag.
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?
A higher coefficient of restitution.
When you're roller skating on level pavement, you can maintain your speed for a long time. But as soon as you start up a gradual hill, you begin to slow down. What slows you?
As you rise your gravitational potential energy increases so your kinetic energy decreases.
Consider an elastic ball that is falling downward toward the ground. The ball hits the ground and then begins traveling upward again. At what point in the trip does the ball have the most energy stored in it as elastic potential energy?
At the bottom of the path when it is not moving, right before it rebounds.
You go through a loop in a roller coaster at constant speed. Where is your apparent weight a minimum?
At the top
Why are black steam radiators better at heating a room than radiators that have been painted white or silver?
Black is the best color for emitting thermal radiation.
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?
Both will give the same momentum.
How would you estimate the temperature of a glowing coal in a fireplace?
By the color of the coal.
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 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 makes the water in the pipes flow faster, dropping the pressure.The faster a fluid moves, the lower the pressure.
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.Bernoulli's Equation in action.
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 forward.
Why does the handle of a metal spoon submerged in boiling soup feel hot ?
Heat from the soup is transferred through the spoon by conduction.
When a fluid is in steady - state flow and its path bends, the pressure on the outside of the bend is always
Higher than the pressure on the inside of the bend.
If you add a little hot tea to ice water at 0 °C, the mixture will end up at 0 °C as long as some ice remains. Where does the tea's extra thermal energy go?
It melts some of the ice.
If you put a warm bottle of wine in a container of ice water, the wine will cool but the ice water won't become warmer. Where is the wine's thermal energy going?
It melts some of the ice.The water-ice mixture remains at 0 °C until the ice is all melted.
An icy sidewalk gradually loses its ice even when the weather stays cold. Where does the ice go?
It sublimes into the air.Sublimation is the phase transition from solid directly to vapor.
Some air fresheners are solid materials that have strong odors. If you leave these air fresheners out, they slowly disappear. What happens to the solid material?
It sublimes into the surrounding air.
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.
You use your breath to inflate a large rubber tube and then ride down a snowy hill on it. After a few minutes in the snow the tube is underinflated. What happened to the air?
Its pressure decreased.Lower temperature means lower pressure.
An object is in stable equilibrium only when
Its total potential energy rises whenever it reorients.
Which temperature scale has 373 as the boiling point of water?
Kelvin
If you put your bathroom scale on a ramp and stand on it, will the weight it reports be high, low, or correct?
Low
While you're weighing yourself on a bathroom scale, you reach out and push downward on a nearby table. Is the weight reported by the scale high, low, or correct?
Low
A popular drink is composed by pouring several types of beverage (one on top of the other) in order to get a layering effect. In what order should the individual beverages be poured into the glass so that your drink is stable?
Most dense first and then in order of decreasing density.
Moving a can of spray paint rapidly in one direction will not mix it nearly as well as shaking it back and forth. Why is it so important to change directions as you mix the paint?
Moving it back and forth gives the paint a constantly-changing acceleration, which means there are forces on the paint as it bumps against the walls of the can.The paint's inertia means it wants to move in a straight line. Changing directions rapidly means large, changing accelerations, and that means large, changing forces on the paint, which makes it mix well. If it were moving steadily there would be no changing forces on the paint.
Why does a pot of water heat up and begin boiling more quickly if you cover it?
No heat is being carried away by evaporating water.
Padded soles in running shoes soften the blow of hitting the pavement. Why does padding reduce the forces involved in bringing your foot to rest?
Padding means greater distortion means the collision lasts longer, and impulse equals force times time.
When a car is stopped, its flexible radio antenna points straight up. But when the car is moving rapidly down a highway, the antenna arcs toward the rear of the car. What force is bending the antenna?
Pressure drag.The air flow around the antenna is turbulent, and pressure drag dominates in that case.
When you hold a lighted match so that its tip is lower than its stick, the flame travels quickly up the stick. Why?
Rising warm air carries heat up the stick.
Suppose you are riding a bicycle. If you want to waste as little energy as possible while the bike is in motion, what type of friction should exist between the bike and the road?
Static
A top is
Statically unstable and dynamically stable.
If you try to cook vegetables in 100 °C air, it takes a long time, but if you cook those same vegetables in 100 °C steam, they cook quickly. Why does the steam transfer so much more heat to the vegetables?
Steam has a higher heat capacity than air.A given volume of steam holds roughly twice as much heat as the same volume of air.
Putting a clear plastic sheet over a swimming pool helps keep the water warm during dry weather. Explain.
Sunlight can penetrate through to the water, and no heat is being carried away by evaporating water.
As you clear the sidewalk with a leaf blower, the blower pushes you away from the leaves. What is pushing on the blower so that it can push on you?
The air coming out of the blower.
If you seal a soft plastic bottle or juice container while hiking high in the mountains and then return to the valley, the container will be dented inward. What causes this compression?
The air inside the container is at a lower pressure than the air outside.The higher pressure causes the container to collapse until the air inside is at the same pressure as the air outside.
Many jars have dimples in their lids that pop up when you open the jar. What holds the dimple down while the jar is sealed, and why does it pop up when the jar is opened?
The air outside is 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 dimple's normal position is out. Only the greater pressure from outside holds it down.
If you place a hot, wet cup upside down on a smooth counter for a few seconds, you may find it difficult to lift up again. What is holding that cup down on the counter?
The air pressure of the air outside the cup.The air inside the cup cools through its contact with the counter, lowering its pressure. The greater pressure outside holds the cup to the counter.
It's often a good idea to wrap food in aluminum foil before baking it near the red-hot heating element of an electric oven. Why does this wrapped food cook more evenly?
The aluminum foil conducts the heat evenly to all parts of the food.
One of the many things that make an artery blockage dangerous is
The amount of fluid passing through the blockage is proportional to the fourth power of the diameter of the opening.
The molecules of antifreeze dissolve easily in water. Why does adding antifreeze to the water in a car radiator keep the water from freezing in the winter and boiling in the summer?
The antifreeze lowers the freezing temperature and raises the boiling temperature of the water.
Most racing cars are built very low to the ground. While this design reduces air resistance, it also gives the cars better dynamic stability on turns. Why are these low cars more stable than taller cars with similar wheel spacings?
The car's low center of mass means a smaller lever arm for the frictional force with the ground.
Bumper cars are an amusement park ride in which people drive small electric vehicles around a rink and intentionally bump them into one another. All of the cars travel at about the same speed. Why are head-on collisions more jarring than other types of collisions?
The collision speed is greatest in a head-on collision.
How does a crowbar make it easier to lift the edge of a heavy box a few centimeters off the ground?
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?
The dimpled ball.The dimples decrease pressure drag.
If the bottom of your bicycle's front wheel becomes caught in a storm drain, your bicycle may flip over so that you travel forward over the front wheel. Explain this effect in terms of rotation, torque, and center of mass.
The force of the drain on the front wheel is very large and the direction of the force passes beneath the center of mass, so it produces an enormous torque rotating the bicycle forward.
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 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?
The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.Decreased potential energy on one side of Bernoulli's Equation means decreased speed on the other.
Why must tall dams be so much thicker at their bases than at their tops?
The greater the depth of the water the greater the pressure pushing on the wall of the dam.At the base of the dam the water is much deeper than at the top, so the pressure is greater.
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.
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 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.
A difficult-to-open jar may open easily after being run under hot water for a moment. Explain.
The heat from the water makes the lid expand and loosen.Generally speaking, metal (like most lids) expands faster with temperature than glass (most jars).
Why is it that you can put a metal pot filled with water on a red-hot electric stove burner without fear of damaging the pot?
The heat is conducted through the pot into the water.Once the water is all evaporated, then the pot can overheat and possibly melt.
You can use a blender to crush ice cubes, but if you leave it churning too long, the ice will melt. What supplies the energy needed to melt the ice?
The kinetic energy of the blender blades.
When you knead bread, it becomes warm. From where does this thermal energy come?
The kinetic energy of your hands.
To free an Apollo spacecraft from the earth's gravity took the efforts of a gigantic Saturn V rocket. Freeing a lunar module from the moon's gravity took only a small rocket in the lunar module's base. Why was it so much easier to escape from the moon's gravity than from the earth's?
The less-massive moon has a much smaller escape velocity than the earth.
When you lie on a spring mattress, it pushes most strongly on the parts of you that stick into it the farthest. Why doesn't it push up evenly on your entire body?
The matress obeys Hooke's Law.
Why do meats and vegetables cook much more quickly when there are metal skewers sticking through them?
The metal skewers conduct heat to the interior of the food.
Oil and vinegar salad dressing settles with the oil floating on top of the vinegar. Explain this phenomenon in terms of density.
The oil is less dense than the vinegar.
You are seated at a table in a Paris Café, contemplating life and watching the bubbles rise upward in your glass of carbonated water. You can think of many physical reasons why those carbon dioxide bubbles should rise upward through the water. Which of the follow observations is not true and therefore does not help explain why the bubbles rise in your Perrier?
The pressure inside a bubble is much less than the pressure in the water around it.
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 fourth power.Blood is a viscous fluid, and Poiseuille's Law governs the flow of viscous fluids.
A baker is decorating a cake by squeezing frosting out of a sealed paper cone with the tip cut off. If the baker makes the hole at the tip of the cone too small, it's extremely difficult to get any frosting to flow out of it. Why?
The rate at which the frosting flows is proportional to the diameter of the hole to the fourth power.Frosting is a viscous fluid, and Poiseuille's Law governs the flow of viscous fluids.
In what way does the string of a bow and arrow behave like a spring?
The restoring force is proportional to the string's distortion.
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?
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.
When you step on a scale, it reads your weight plus the weight of your clothes. Only your shoes are touching the scale, so how does the weight of the rest of your clothes contribute to the weight reported by the scale?
The scale responds to the entire downward force exerted on it.
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.On a bitter cold day the snow will be at a temperature well below freezing.
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 speed change is the same during each of the 5 seconds.
When two trains are traveling side by side at breakneck speed, it's still possible for people to jump from one train to the other. Explain why this can be done safely.
The speed of the two trains relative to each other is small.
As a skateboard rider performs stunts on the inside of a U-shaped surface, he often leans inward toward the middle of the U. Why does leaning keep him from falling over?
The support force from the surface of the U is at an angle, and leaning keeps his center of mass in line with the support force.
Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun rises near the seashore.
The surface wind will blow from the water toward the land.
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 has almost no turbulent wake. The drag on it is mostly viscous drag.
When you mix milk or sugar into your coffee, you should move the spoon quickly enough to produce turbulent flow around the spoon. Why does this turbulence aid mixing?
The turbulence causes the coffee to move quickly in random directions, aiding mixing.
How does running directly behind another runner reduce the wind resistance you experience?
The turbulent wake behind the other runner shields objects in that wake from the air flow around the other runner.
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.
Many grocery stores display frozen foods in bins that are open at the top. Why doesn't the warm room air enter the bins and melt the food?
The warm air is blocked from the food by the cold air above the food.This is true because cold air is denser than warm air and so stays close to the food.
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 goes from high speed and low pressure to low speed and high pressure when it hits the bucket.
For an object that sinks in a fluid,
The weight of fluid displaced is less than its weight.
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?
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.
Why do elastic balls bounce so well?
They store energy through compression, like a spring.
Astronomers can tell the surface temperature of a distant star without visiting it. How is this done?
They use the color temperature of the star's light.The color of the light from the star corresponds to a particular temperature.
You are riding an amusement park ride where you are strapped to the inside of a giant metal wheel that is rotating quite rapidly. Your acceleration is
Toward the center
Suppose you have gotten a new job where you have to design balls that fly through the air with as little resistance as possible. You know that in front of the ball there is laminar flow, so in back of the ball there should be
Turbulent flow, because there will be less drag.
When a fish is floating motionless below the surface of a lake, what is the amount and direction of the force the water is exerting on it?
Upward, equal to the weight of the fish.The buoyant force from the water exactly balances the weight of the fish.
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.Thus the pasta is cooking in cooler water in Denver than in New York.
Why are failures in dams more likely to occur closer to the bottom of the dam?
Water pressure is higher at the bottom.
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.
When sliding a heavy box across the floor, it is often times helpful to lift up on it slightly because
You are lessening the friction force by reducing the contact force between the box and the floor
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.
You are riding a multi-speed bicycle up a steep hill that's 100 m high and want to do as little work as possible on your way up the hill.
Your choice of gears doesn't matter because you'll do the same amount of work climbing the hill no matter which gear you choose.
Wind is one of nature's ways of transferring energy through
convection
Aerodynamic forces consist of
drag and lift.
A curve ball in baseball curves because of
drag forces.
As the Reynolds number increases,
flow is going from being viscous dominated to inertia dominated and therefore turbulent.
Suppose you have two containers with liquid in them. One has a density of 760 kg/m3 and the other has a density of 910 kg /m3. If an object floats in one container and sinks in the other, the density of the object
has a value between 760 kg/m3 and 910 kg/m3.
You are taking a shower in your dormitory when someone flushes a toilet nearby. The pressure in the cold water line drops and you find yourself showering in what feels like molten lava. This loss of cold water pressure occurs when the toilet lets cold water flow through the pipes delivering it to the bathroom and the water's speed in those pipes increases. Assuming all the piping to be about on the same level, the cold water's faster motion in the delivery pipes reduces its pressure in the shower head because faster moving water
has less pressure than slower moving water.
You are a mechanic in a garage and are working on a carburetor that is made of metal, has a glass inspection window and plastic gears for the choke. If all three types of material are at the same temperature and each type of material is in contact with the other two, then
heat will flow from the metal to the glass, and from the glass to the plastic.
A stream of smoothly flowing water arcs through the air and hits the side window of a house. At the surface of the window, right where the stream of water hits it, the water's pressure is
higher than atmospheric and the water's speed is slower than in the stream.
Flowing honey is less likely to become turbulent than flowing water because
honey's large viscosity favors laminar flow.
You stop for a cappuccino at a coffee shop and notice that the tiny white bubbles of steamed milk remain on the surface of the coffee. These air-filled bubbles stay where they are, rather than descending into the coffee or rising into the air, because they are
less dense than the coffee but more dense than the air above the coffee.
Suppose you are standing on a bathroom scale when you are flying in a jet airplane. For a moment the scale reads less than your actual weight. During that moment, it's exerting an upward force on you that is
less than your weight- a scale reflects the amount of weight exerted on it, so if it reads less than your actual weight, that means it is exerting a force on you that is less than your weight.
If a golf ball were smooth rather than dimpled, it would
not travel as far after being hit by a golf club.
A pedestrian bridge crosses a street. This bridge is entirely supported by columns from below. A gap at each end of the bridge separates the bridge's surface from the sidewalks leading to the bridge. The width of each gap changes with time. This width is smallest
on hot days.
You are trying to deliver water to a sink in the tree house in your backyard. You run an old hose from the spigot behind your home, across your yard, and up the tree to a sink inside the tree house. You let water fill the hose all the way to the tree house sink and then leave the hose pressurized overnight, with no water flowing in it. Unfortunately, the hose cannot tolerate high pressure anymore and it springs a leak around midnight. By morning your whole backyard is a swamp. The most likely site for the leak is
on the ground—the lowest point on the hose.
You go to an amusement park and, being in a physics class, you have connections. The management lets you stand on a scale as you ride a Ferris Wheel that rotates fairly rapidly. You will notice the lowest reading on the scale
on top, because the normal force upwards is weaker than your weight.
Low-E coatings are placed on house windows because
radiative heat transfer is a big problem for clear windows but the Low - E coating reflects infrared light.
Dimples on a golf ball hit without spin
reduce drag
The top surface of a calm, smoothly flowing stream is always at atmospheric pressure. As water in this stream runs into a tree stump and slows almost to a stop, the water's top surface
shifts upward slightly above the normal stream level.
A three - wheeler is
statically stable and dynamically unstable
A motorcycle is
statically unstable and dynamically stable
A classroom demo that is popular with students and unpopular with custodians is to fill a Styrofoam cup with water, poke a hole in the bottom and then drop the cup into a garbage can waiting below. On the way down, the leak will
stop because the cup and water are both in free fall and locally weightless.
Some scientists assert that there would be no life on earth if ice did not have a molecular structure with a lot of open space because
the density of ice would be greater than water and lakes would freeze solid - from the bottom up.
When you drop a rubber ball on the floor and it bounces, the direction of its velocity reverses because
the floor exerts an upward support force on the ball and this force stops the ball's descent and eventually propels it upward.
It's much easier to carry a weight in your hand when your arm is at your side than it is when your arm is pointing straight out in front of you. Use the concept of torque to explain this effect. When you arm is at your side
the force is parallel to the lever arm, not perpendicular.
You are filling a jar of honey from the spigot at the bottom of a large barrel at the grocery store. The honey flows extremely slowly, so the store manager has the barrel refilled. Now the honey flows much more rapidly from the spigot because
the pressure of the honey at the bottom of the barrel increases as the height of honey in the barrel increases.
A space vehicle uses a large black surface to radiate away waste heat. How does the amount of heat radiated away depend on the area of that radiating surface? If the surface area were doubled how much more heat would it radiate, if any?
the radiated heat will be 2x larger
Suppose you have an aquarium and you notice that you have a solid plastic decoration and a rock of about the same volume but twice as dense, and both are totally submerged in the water. The buoyant force on the plastic object is about ___________as that on the rock.
the same.
Stamping your feet cleans the snow off of them because
the snow on your feet has inertia.
The spin cycle in your washing machine partially dries clothes by spinning them in a perforated metal basket. Such a process works because
the water leaves the basket moving tangent to the circular path
The reason fast-moving water makes noise is
turbulence
You are flying on an airplane and you notice that a ball of aluminum foil from lunch starts to roll to the left. From the motion of the foil ball you can conclude that the plane is
turning toward the right.
The four things that affect the amount of water flowing through a hose are
water viscosity, hose length, inlet and outlet pressures and hose diameter.
