physics test 2
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
As you push downward on a ball with your open palm, it
Accelerates with your palm and pushes upward on your palm
As your car reaches the top in a smoothly turning Ferris wheel, which way are you accelerating?
Downward
summary of bouncing balls
Each ball has a coefficient of restitution. Energy lost in a bounce becomes thermal. The bouncing surface can effect a ball's bounce.Surfaces bounce, too.
If you place a tennis ball on a basketball and drop this stack on the ground, how high will the tennis ball bounce?
Much higher than its original height
Pressure and Particle Density
Particle density: number of particles per unit volume Particles in a gas contribute equally to pressure. -Lower-mass particles move faster and bounce more, so all the effects of particle mass cancel out. Gases with equal particle densities and equal temperatures have equal pressures.
The time it takes a relatively small object to orbit a much larger object doesn't depend on the mass of the small object. Use an astronaut who is walking in space near the space shuttle to illustrate that point.
The astronaut and shuttle have vastly different masses, but both orbit the much-larger earth at the same rate.
Does a 3-meter deep lake or a 6-meter deep small pond exert more pressure on a dam?
The six-meter deep small pond
A upright tricycle is in a stable equilibrium because tipping it
increases its potential energy.
Water seeks its level (flows until it is the same height everywhere) because that arrangement
minimizes the water's total potential energy
You are standing on a bathroom scale in an elevator. As the elevator starts moving upward, the scale reads
more than your weight
Rockets receive their forward propulsion through
pushing against the exhaust
A "bouncy" or "lively" ball bounces higher from a rigid, immovable surface than a "dead" ball does because the "bouncy" ball
returns more collision energy as rebound energy.
When you are riding a carousel that is turning at a steady rate, your acceleration is
toward the center of the carousel.
When you put water in a kitchen blender, it begins to travel in a 5.2-cm-radius circle at a speed of 5.9 m/s. How hard must the sides of the blender push inward on 0.0026 kg of the spinning water?
F = 1.7405 N
If you and a friend 11 m away each have masses of 67 kg, how much gravitational force are you exerting on your friend?
F = 2.47 N x 10^-9
How would raising the height of a sport utility vehicle affect its turning stability?
Make it more likely to tip over
Which object is exerting the stronger gravitational force on the other, the earth or the moon, or are the forces equal in magnitude?
The force of the earth on the moon is equal to the force of the moon on the earth.
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.
Why is a stationary tricycle so stable?
The tricycle is in a stable equilibrium
Water accelerates toward lower pressure and is incompressible? (true or false)
True
Do the ship and fuel have opposite momentums? (rockets)
Yes -The greater the fuel mass and backward velocity, the greater the ship's forward momentum
When you put water in a kitchen blender, it begins to travel in a 4.8-cm-radius circle at a speed of 7.3 m/s. How quickly is the water accelerating?
a = 1110 m/s^2
centripetal acceleration and force
acceleration: center-directed. gives rise to feeling of acceleration. Points away from the center of motion and is a sensation due to inertia, not a real force (also known as centrifugal force) force: caused by center-directed
When a baseball bounces from a moving bat, the final speed of the baseball
can exceed the initial speed of either object.
When you drink water through a straw, the water
is pushed upward by a pressure imbalance
How does the rocket use gas to obtain thrust?
it redirects gas's thermal motion into a directed jet
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.
You can balance a broom on your hand if you're careful. To do this trick well, you must look at
the broom's center of gravity.
Astronauts in the space shuttle feel weightless because
they are in a constant state of free - fall.
A helium balloon has mass, yet it doesn't fall to the floor. Is there a real force pushing up on the helium balloon?
yes
Why do you feel flung outward on a carousel?
you are accelerating inward on the carousel -riders undergo uniform circular motion (follows a circular path at a constant speed & accelerates towards circles center)
If a ball's energy ratio is 0.5 and it drops onto a rigid floor, how high will it bounce, relative to the height from which it dropped?
100% or 50%??? idk
Two cars are traveling at 60 mph and 50 mph, respectively, according to a pedestrian. The range of possible collision energies for these two cars extends over a factor of
121
You and your family are on a trip to the local museum and you notice that in the aquarium there are four fish: fish 1 is floating, fish 2 is stationary 2m below the water's surface, fish 3 is stationary 4 m below the water's surface and fish 5 is on the sand at bottom of the tank. (Note: things don't look good for fish 1 and fish 4 but that's beside the3 point here) Your Mom says that she'll buy you lunch if you rank the densities of the fish in order of increasing density, including the density of water in your ranking. Please select your ranking below.
1<2=3=water<4
If a ball's coefficient of restitution is 0.5 and it drops onto a rigid floor, how high will it bounce, relative to the height from which it dropped?
25% of the drop height
Escape velocity at the surface of the Earth is about:
25,000 mph
Escape velocity at the surface of the Earth is about
25,000 mph (11 km/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 what is its acceleration?
4 m/s2
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
What is the gravitational force that two 100 kg persons exert on each other when standing 1m apart?
6.672x10-7 N
Why doesn't the atmosphere fall or collapse?
A gradient in its pressure supports its weight Air has a density: it has mass per volume.
Air and pressure
Air consists of individual atoms and molecules -Thermal energy keeps them separate and in motion -Air particles bounce around in free fall, like tiny balls Air particles transfer momentum as they bounce
Air temperature on an absolute vs conventional scale
Air's temperature on a conventional scale is: related to average thermal kinetic energy per particle Air's temperature on an absolute scale is: proportional to average thermal kinetic energy per part SI unit of absolute temperature: kelvins or K
Orbits
An object that starts with a sideways velocity can miss the Earth as it falls Orbits can be -closed loops: circles and ellipses -open arcs: parabolas and hyperbolas
As a comet approaches the sun, it arcs around the sun more rapidly. Explain.
An orbiting object sweeps out equal areas in equal times. Closer to sun requires faster speed.
What makes a spaceship orbit the Earth?
An orbiting spaceship falls but misses the Earth.
Archimedes' Principle
Any object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces
Hot Air Balloon
As the temperature of air increases, its particles move faster, bounce harder, and bounce more often. They also contribute more to air's pressure A balloon filled with hot air at ordinary pressure contains fewer particles than the air it displaces and weighs less than the air it displaces and experiences a buoyant force that exceeds its weight
As water flows upward and downward through a pipe?
As water flows upward in a uniform pipe, its speed can't change (a jam or a gap would form) so its gravitational potential energy increases and its pressure potential energy decreases As water flows downward in a uniform pipe, its speed can't change so its gravitational potential energy decreases and its pressure potential energy increases
As water flows upward and downward through a water fountain?
As water rises upward from a fountain nozzle, its pressure stays constant (atmospheric) so its gravitational potential energy increases and its kinetic energy decreases As water falls downward from a spout, its pressure stays constant (atmospheric) so its gravitational potential energy decreases and its kinetic energy increases
Energy transformation: water horizontal fountain
As water sprays horizontally from a nozzle, its height is constant (PE = m g h = constant), its kinetic energy increases, and its pressure potential energy decreases As a horizontal stream of water hits a wall, its height is constant, its kinetic energy decreases, and its pressure potential energy increases
You are riding a very fast Ferris Wheel so that you actually notice a variation in your apparent weight. Where is your apparent weight maximum?
At the bottom
You go through a loop in a roller coaster at constant speed. Where is your apparent weight a minimum?
At the top
Pressure Imbalances
Balanced pressures exert no overall force Unbalanced pressures exert an overall force
How does a moving bat drive a ball forward?
Ball bounces off bat, in bat's frame of reference -When bat and ball are moving toward one another, collision speed is their speed of approach rebound speed is their speed of separation -The bat's inertial frame of reference is the perspective (or point of view) in which bat's center of mass appears motion less and the ball appears to bounce off the motionless bat
How does pushing on the plunger of a syringe cause medicine to flow into a patient through a hollow hypodermic needle?
Bernoulli's Equation: pressure on the fluid converts to kinetic energy (motion) of the fluid
If you submerge a 5-kg log in water and it displaces 9 kg of water, what will the net force on the log be the moment you let go of the log?
F = 39.2 N
Why does the floor's surface affect the bounce?
If the floor dents, it also receives collision energy -The denting floor stores and returns energy.Floor also has an energy ratio that affects the bounce. -Impact forces on ball & floor: equal but oppositeWork done on each is proportional to its dent.Fraction of collision energy is proportional to its dent.
Pascal's Law
In a closed system, pressures transmitted to a fluid are identical to all parts of the container. Variations in the pressure are due only to the depth of the fluid. This principal is vital to mechanical devices like hydrolic lifts and brakes
Water enters your home plumbing at ground level. Where will you get the strongest spray from a shower?
In the basement shower
Why does a moving tricycle flip during turns?
Inertial effects overwhelm its static stability -during a turn, wheels accelerate to the inside (Upright rider is almost inertial (coasts forward) so tricycle and rider begin to tip) -tricycle drives out from center of gravity
Why doesn't a ball rebound to its original height?
It wastes some of its energy during the bounce. -While slowing as it hits a rigid floor, a ball's kinetic energy decreases by the collision energy elastic potential energy increases as it dents -While rebounding from the floor, the ball's elastic potential energy decreases as it un-dents kinetic energy increases by the rebound energy
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.
Lead sinkers actually float on the surface of liquid mercury. Which takes up more space: 1 kg of mercury or 1 kg of lead?
Lead
Law of Areas
Line from the sun to a planet sweeps with equal areas in equal time. A planet will move through equal area of space in an equal amount of time
Mars has a larger orbital radius than the earth. Compare the solar years on those two planets.
Mars' orbital year is longer than the earth's.
Why is atmospheric pressure lower in the mountains than it is at sea-level?
Mountain air has less air above it to support.
What keeps a rocket pointing forward?
On the ground, a rocket needs static stability In the air, a rocket needs aerodynamic stability In space, a spaceship is a freely rotating object
Perihelion and Aphelion
Perihelion- closest to sun -When a planet is in perihelion its orbital velocity increases Aphelion- farthest from sun -When a planet is in aphelion its orbital velocity decreases
Kepler's Laws of Planetary Motions
Planets move in elliptical orbits with the sun at one of the foci
Why aren't there any thermometers that read temperatures down to -300 ºC?
That would be lower than absolute zero.
A marshmallow is filled with air bubbles. Why does a marshmallow puff up when you toast it?
The air in the bubbles gets warm and expands.
You seal a rigid container that is half full of hot food and put it in the refrigerator. Why is the container's lid bowed inward when you look at it later?
The air pressure of the air outside the container pushes the lid in.
In some roller coasters, the cars travel through a smooth tube that bends left and right in a series of complicated turns. Why does the car always roll up the right-hand wall of the tube during a sharp left-hand turn?
The apparent weight is down and to the right.
A salad spinner is a rotating basket that dries salad after washing. How does the spinner extract the water?
The apparent weight of the water is outward, forcing it through the holes in the basket.
What keeps the air molecules in our atmosphere from piling up on the ground?
The atmosphere's thermal energy
When a soft, elastic ball drops onto a rigid floor, which object(s) has significant work done on its surface, as viewed from the perspective of that object s object s' center of mass?
The ball only
Why is a stationary bicycle so unstable?
The bicycle is in a unstable equilibrium
Law of Periods
The farther a planet is from the focus, the longer the period of revolution -P2 is proportional to a3 -Ex: Earth is closer to the sun than Jupiter, therefore the Earth has a shorter period of revolution
A hammer's weight is downward, so how can a hammer push a nail upward into the ceiling?
The force stopping the hammer is downward so the force on the nail is upward.
Ice tea is often dispensed from a large jug with a faucet near the bottom. Why does the speed of tea flowing out of the faucet decrease as the jug empties?
The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.
Why must tall dams be so much thicker at their bases than at their tops?
The greater the depth of the water the greater the pressure pushing on the wall of the dam.
Wasp and hornet sprays proudly advertise just how far they can send insecticide. How does the pressure inside the spray can affect that distance, and why is the direction of the spray important (vertical vs. horizontal)?
The greater the pressure, the farther it will spray. A vertical spray will only go up or down, so you need to spray at least a little horizontally to get any distance.
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 work with a catering firm and have been given a challenge. By emptying several liquid beverage dispensers, you have to rank them in order of their content (which one is fullest, next fullest, etc.) Having had a physics class, you simply open the horizontal spouts all from the same height and compare where the streams land on the ground below. In terms of how far each stream lands from the jug, which of the following statements is correct:
The pressure (and hence water level) is lower when the speed is lower. Lower speeds result in smaller ranges and the streams will land closer to the jug.
When you stand in a pool with water up to your neck, you find that it's somewhat more difficult to breathe than when you're out of the water. Why?
The pressure due to the depth of the water above your chest presses in on you.
Each time you breathe in, air accelerates toward your nose and lungs. How does the pressure in your lungs compare with that in the surrounding air as you breathe in?
The pressure in your lungs is less than that of the surrounding air.
Blood flows through a section of a horizontal artery that is partially blocked by a deposit along the artery wall. A hemoglobin molecule moves from the narrow region into the wider region. What happens to the pressure acting on the molecule as it moves from the narrow into the wider region?
The pressure increases
What limits a spaceship's speed, if anything?
The rocket's fuel to spaceship ratio - Spaceship's ultimate speed increases as the ratio of fuel mass to ship mass increases & the fuel exhaust speed increases
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.
For an object that sinks in a fluid,
The weight of fluid displaced is less than its weight.
Suppose you are spending your weekend on roller skates trying to get momentum from somewhere. Which of the following will give you momentum in the north direction?
Throwing your keys southward.
Why must you lean a bicycle during turns?
To balance inertial effects with static instability -during the turn, the wheels accelerate to the inside
As the moon orbits the earth, which way is the moon accelerating?
Toward the earth.
Closer to the sun, faster the velocity because of the gravitational pull (True or False)
True
Law of Universal Gravitation
Two masses attract one another with gravitational forces equal in amount to the gravitational constant times the product of their masses, divided by the square of their separation
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.
If your boat weighs 1200 N, how much water will it displace when it's floating motionless at the surface of a lake?
Vdisplaced = 0.122 m^3
Why are failures in dams more likely to occur closer to the bottom of the dam?
Water pressure is higher at the bottom.
Buoyant Force
When any object is wholly or partially immersed in fluid, the upward force given by the fluid is BUOYANT force
how do you stay seated on a loop-the-loop?
You are accelerating downward very rapidly (acceleration is strongly downward but your feeling is strongly upward)
Suppose you had a very long straw that could reach from a cup of water on the ground level to the top of a very tall building. What happens when you suck on the straw in order to bring water up?
You could bring the water up to only a certain height in the straw because the atmosphere pushes down on the surface of the water by a given amount.
What aspects of motion do you feel? (rollercoaster)
You feel acceleration but not velocity -This feeling of acceleration is not a real force -You feel an overall apparent weight (feeling of real weight plus acceleration)
The total energy of a portion of water in steady state flow is constant
along a streamline.
If there were no launch pad beneath the space shuttle at lift shuttle at lift-off, the upward thrust of its engines off, the upward thrust of its engines would be
approximately unchanged.
Your apartment window opens 20 meters (65 feet) above a lemonade stand. Your friend lowers a long plastic tube out the window until its end enters the tank of delicious lemonade far below. She then begins to suck on the other end of the tube in hopes of getting a free drink. To her dismay, she never tastes a drop because
atmospheric pressure cannot support a column of lemonade 20 meters tall.
One can ride a bicycle without hands because it
automatically steers under your center of gravity.
As a drinking straw is made taller and taller, drinking water through it
becomes harder and eventually impossible.
Two cars are traveling at 60 mph and 50 mph, respectively, according to a pedestrian. When they collide, their approaching speed will be
between 10 mph and 110 mph.
If you could take all the air out from inside an opened plastic bottle, its sides would
crush inward extensively
Suppose water from a tall tower supplies a nearby home. If water faucets upstairs and downstairs are turned fully on, will more water per second flow from the downstairs or the upstairs faucet? Or will water flow in each be the same?
downstairs Water pressure depends on the depth below the free surface. Downstairs faucets are simply "deeper" and receive greater pressure, which means greater rate of water flow
A dropped ball accelerates downward at the acceleration due to gravity. If you push downward on a ball with your open palm, it will accelerate downward
faster than the acceleration due to gravity.
Astronauts in a space shuttle accelerating uniformly in a straight line far away from any planet or star would
feel just like there is local gravity
All current rockets eject stages or booster rockets as they climb from the earth's surface up to orbit. A rocket that did not eject any stages or booster rockets while climbing from the ground to orbit would
have to have a launch weight that was about 90% rocket fuel.
Air and Density
increases the air's density: its mass per volume increases the air's pressure: its force p
The total energy of a portion of water in steady state flow (laminar flow) is constant
is pushed upward by a pressure imbalance
Why can you ride a bicycle without hands?
it automatically steers under center of gravity -When bicycle begins to lean, it steers because the fork pivots to reduce total potential energy & ground's torque on front wheel causes precession
The force a spring exerts on one of its ends is proportional to
its distortion away from equilibrium.
What pushes a rocket forward?
its gaseous exhaust pushes it forward -momentum is initially zero & remains zero
How does air inflate a rubber balloon?
its pressure pushes the balloon's skin outward Air is a gas: individual atoms and molecules Air has pressure: it exerts a force on a surface Pressure inside a balloon is greater than outside
Compared to planets close to the sun, and based upon Kepler's third law of planetary motion, the length of the year of planets farther out from the sun are
larger
An object that is in equilibrium is
motionless or moving at constant velocity
You are a passenger in a car that is turning left and you find yourself thrown against the door to your right. Is there a force pushing you toward the door?
no
A hydrogen gas particle weighs half as much as a helium gas particle. If you replace the helium in a balloon with hydrogen, it will be able to lift
slightly more weight than it did with helium
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
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
For an object that is neutrally buoyant in a fluid,
the weight of the fluid displaced equals the object's weight.
A diver stands motionless at the end of a spring board, which bends downward. If her identical twin joins her, how far downward will the board then bend?
twice as far
A new skyscraper supplies water to all of its floors through a single vertical pipe. When someone opens the faucet on the ground floor,
water rushes out at hundreds of miles per hour.
If a tricycle is on a sloping floor, will this rule about it being in a stable equilibrium as long as its center of gravity is above its base of support still work?
yes
Once in space, does a spaceship have weight?
yes, but less than at ground level
Why do you feel heavy as a roller coaster turns?
your feeling of acceleration is outward (acceleration is inward but your feeling is outward)
Why do you feel light as a roller coaster dives?
your feeling of acceleration is upward. (your acceleration is downhill but, your feeling of acceleration is uphill)
When you are in free fall, your apparent weight is
zero
Spaceship Spaceship-1 launches into orbit around the earth while Spaceship Spaceship-2 launches vertically and travels purely up and down. At their peak altitudes, the speed of Spaceship Spaceship-1 is approximately
∞ (infinity) times the speed of Spaceship (infinity) times the speed of Spaceship-2.