Section 1
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Water weighs about 10 N per liter. A 4.0 kg ball floats on the water's surface. What is the weight of the water being displaced by the ball?
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Cards (119)
Section 1
(50 cards)
Water weighs about 10 N per liter. A 4.0 kg ball floats on the water's surface. What is the weight of the water being displaced by the ball?
About 40 N
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.
If you sit in a good swivel chair with your feet off the floor, the chair will turn slightly as you move about but will immediately stop moving when you do. Why can't you make the chair spin without touching something?
Changing a system's angular momentum requires an angular impulse
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
For an object that is neutrally buoyant in a fluid,
The weight of the fluid displaced equals the object'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.
What is the gravitational force that two 100 kg persons exert on each other when standing 1m apart?
6.672x10-7 N
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
For an object that is floating on a fluid,
The weight of the fluid displaced equals the object's weight.
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.
Suppose you are standing on a bathroom scale when you are flying in a jet airplane. For a moment the scale reads more than your actual weight. During that moment, it's exerting an upward force on you that is greater than your weight and you are
accelerating upward.
Water settles to the bottom of a tank of gasoline. Which takes up more space: 1 kg of water or 1 kg of gasoline?
The water sinks because it's more dense. More dense means more compact, so gasoline takes up more space. 1 kg of gasoline because gasoline is less dense than water.
Water weighs about 10 N per liter on Earth. A 4.0 liter ball is pushed underwater on the space shuttle, where gravity was 1/10 that on Earth. What is the buoyant force on the ball?
4 N
Firefighters slide down a pole to get to their trucks quickly. What happens to their gravitational potential energy, and how does it depend on the slipperiness of the pole?
It converts to kinetic energy and thermal energy of their hands and the pole. A slippery pole will result in more kinetic and less thermal energy
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?
While the refrigeration helps, there is something more fundamental going on. Consider the density of cold air compared to that of warm air.
If you pull slowly on the top sheet of a pad of paper, the whole pad will move. But if you yank suddenly on the sheet, it will tear away from the pad. The reason for these different behaviors is
the pad has inertia.
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
When you apply the brakes on your bicycle, which way do you accelerate?
Backward.
Stamping your feet cleans the snow off of them because
the snow on your feet has inertia.
As you jump across a small stream, does a horizontal force keep you moving forward? If so, what is the force?
A force is a push or a pull. As you leaped you pushed against the ground, but that push ended the instant your feet left the ground.
Gravity creates
Pressure gradients in fluids
When a star runs out of nuclear fuel, gravity may crush it into a neutron star about 20 km (12 miles) in diameter. Although the star may have taken a year or so to rotate once before its collapse, the neutron star rotates several times a second. Explain this dramatic increase in angular velocity
The angular momentum of the star is conserved.
Why aren't there any thermometers that read temperatures down to -300 ºC?
Absolute zero is about -273 °C. That would be lower than absolute zero.
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
When sitting still on the ground, a tricycle is in a state of
stable static equilibrium
As the moon orbits the earth, which way is the moon accelerating
Both will give the same momentum.
Why can't an acrobat stop himself from spinning while he is in midair?
His angular momentum is conserved.
Why can't you open a door by pushing its doorknob directly toward or away from its hinges?
The force here is parallel to the lever arm, not perpendicular.
Why will a rolled - up ball of aluminum foil float in water but solid aluminum will sink
Due to the air inside, the average density of the ball is lower than water
Steep mountain roads often have emergency ramps for trucks with failed brakes. Why are these ramps most effective when they are covered with deep, soft sand?
The sand converts most of the energy of its collision with the truck's wheels into thermal energy.
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
Some fish move extremely slowly, and it's hard to tell whether they are even alive. However, if a fish is floating at a middle height in your aquarium and not at the top or bottom of the water, you can be pretty certain that it's alive. Why?
If the fish is floating at a middle height, it must be be regulating its density to be equal to the density of the water, which a dead fish couldn't do.
If you pull down on the basket of a hanging grocery store scale so that it reads 15 N, how much downward force are you exerting on the basket?
15 N
If a motorcycle accelerates too rapidly, its front wheel will rise up off the pavement. During this stunt the pavement is exerting a forward frictional force on the rear wheel. How does that frictional force cause the front wheel to rise?
But what causes the front wheel to lift? Examine the torque produced by the frictional force relative to the center of mass.
Astronauts in the space shuttle feel weightless because
they are in a constant state of free - fall
It is important for cyclists to lean their bicycles while negotiating sharp turns because
the torque created by their leaning balances out the frictional torque from the road which would tend to flip them
Falling into a leaf pile is much more comfortable than falling onto the bare ground. In both cases you come to a complete stop, so why does the leaf pile feel so much better?
It takes more time to come to rest falling in a leaf pile, so the stopping force is less
Some athletic shoes have inflatable air pockets inside them. These air pockets act like springs that become stiffer as you pump up the air pressure. High pressure also makes you bounce back up off the floor sooner. Why does high pressure shorten the bounce time?
A stiffer spring means less distortion, which takes less time
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?
A less-dense liquid will float on top of a more-dense liquid. The upper liquid is less dense than the lower liquid.
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?
The buoyant force from the water exactly balances the weight of the fish. Upward, equal to the weight of the fish.
The back of your car seat has a head rest to protect your neck during a collision. The type of collision which causes your head to press against the headrest is
a rear-end collision
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
You are camping in the breathtaking mountains if Colorado. You spy an unopened diet soda can floating motionless below the surface of a lake. What is the direction and amount of force the water exerts on it?
Up, equal to the can's weight
Why can't you open a door by pushing on its hinged side?
The lever arm is zero.
Your apparent weight is equal to your weight
In an elevator not accelerating
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.
How far apart would two 100 kg persons need to be so that the force they exert on each other is equal to 1N? You can assume they are point masses, having mass but no size.
8.17 × 10-4 m
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.
Loose objects on the dashboard slide to the right when the car turns suddenly to the left because
However, the objects are in motion and so tend to continue moving straight while the rest of the car moves left.
Section 2
(50 cards)
a ball falls from rest for 5 seconds. neglectiong air resistance, during which of the 5 seconds does the balls speed increse most?
the speed change is the same during each of the 5 seconds.
why must the surface of a hammer be very hard and stiff for it to drive a nail into wood
a stiffer surface means less distortion, which takes less time which means the force on the nail is greater
suppose you go from the earth to a planet where the acceleration of gracity is 5 m/s2. on the new planet your weitght will be about
be 1/2 its value on earth
when an automobile is braked to a stop its kineticenergy is transformed to
thermal energy
you attach a graphing calculator to a rubber band and rpeadtedly bounce it up and down vertically. when the rubber band is at its maximum strecth away from your hand
the calculators velocity is zero but its acceleration is upward
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 the compression
the air inside the container is at a lower pressure than the air outside
A horse does work on a cart it's pulling along a straight, level road at a constant speed. The horse is transferring energy to the cart, so why doesn't the cart go faster and faster? Where is the energy going?
The energy is converted to thermal energy as the wheels, axles, and ground get warmer
your weight is
the gravitational attraction force between you and the earth
when you throw the ball it travels in an arc toward the hoop. ignoring any forces that air exerts on the ball, the net force on the ball just after it leaves your hand is
straight down
suppose an object is traveling at terminal velociy so it is falling through air but not accelerating. how does the force of air resistance compare to its weight
the two forces are equal and opposite
suppose the moons angular velocity is halved. by what factor will its rotational kinecitc energy change
it will decrease to 1/4 its original value
A baseball player balances a bat on his finger; the bat is laying sideways and not standing on end. The bat will balance
at its center of mass.
which system is in a state of stable static equilibrium
a marble in the bottom of a spherical bowl
why is your velcoity continuously changing as you ride on a carousel?
because your directions of motion is continously changing
if you push for a half hour or a whole hour against a stationary wall
no work on the wall is done in either case
a feather and coin droppped in a vaccum fall with equal
accelerations
which does more work in lifting a grain of rice over its head. an ant or a person?
the person does more work.
you are floating in a hot air balloon. you look up and notice that the bottom of the balloon is open. neglecting any diffusion of molecules, hot air remains inside the balloon despite this opening because
convection naturally would make hot air rise, so it has no opening through which to escape
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 kilograms is a measure of an objects
mass
suppose you are driving north and suddenly hit your brakes to avoid a dog. as you come to a stop your acceleration is directed
south
as your car reaches the top of the ferris wheel, which way are you accelerating
downward
what type of friction causes bearings to not waste much energy
static
the force exerted on the tires of a car to directly accelerate it along a road is exerted by the
road
suppose a tree branch falls down to the ground with constant accleration and takes 2 seconds to hit the ground . which of the following statemtents regarding the path of the branch is true
it cobers more distance during the last second
you are riding on a merry go round and you move out to the edge. the rotational mass of the sytem
increased
if you push an object twice as far while applying the same force you do
twice as much work
you are swinging a tin can around your head in perfectly horizontal circle and its accelerations is 32 m/s2. if its spped is 4 m/s what is the value of the radius of its circular path
.5 m
you are driving yoru car down the highway at constant velocity. which is true
both the cars kinectic energy and monentum are constant
why do elastic balls bounce so well
they store energy through compression like a spring
when a twirling ice skater brings her arms inward her rotational speed
increases
Consider an elastic ball that is falling downward toward the ground. the vall hits the ground and then begins traveling upward again. at what point in the triop 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.
If you need to harness energy in order to do a particular job, the type of energy needed is
ordered energy
the skier is traveling in a straight line at constant speed. the net force she experiences is ?
zero
cities can use water towers to supply pressurized water to homes because
water pressure at the bottom of the tower is much higher than at the top
When you begin to walk forward, the force that allows you to accelerate is
the friction force of the ground exerted on your feet.
you are driving down the highway and speeding up. which is true
neither the cars kinectic energy nor momentum is constant
as the truck rolls up the ramp, it slows to a stop. what happens to the trucks kinetic energy, its energy of motion?
it converts into gravitational potential energy
rockets recieve thier forward propulsion through
pushing against the exhasut casuing the eshaust to push against the rocket
when a rifle is fired it recoils as the bullet is set in motion. the rifle and bullet ideally acquire equal
but opposite amounts of momentum
a bathroom scale reads
your apparent weight
imagine sitting on a merry go round and riding along as it spins. assuming you are not grabbing it anywhere and are not moving with respect to ther platform
static friction (directed inwards) cause you to accelerate
the earth exerts a downward force of 850 N on the astranut. what force if any does the astranut exert on the earth?
850 N upward
you accidentally miss the doorway and run into the wall. you suddenly experience a backward force that is several times larger than your weight. the reason this force is so large is?
your acceleration is huge as you stop so suddenly
why must tall dams be so much thicker at their bases than at thier tops
the greater the dpth of the water the greater the pressure pushing on the wall of the dam
Describe the process of writing with chalk on a blackboard in terms of friction and wear.
Sliding friction between chalk and blackboard causes wear on the chalk.
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
The rate at which energy is used, stored, created, dissipated, etc
Power
you have t opush the saw away from you as it moves away from you and pull the sawtoward you as it moves toward you. when are you doin positive work on the saw
both while pushing and pulling
A child is riding a bike and skids to a stop. What happens to their kinetic energy?
It is turned into heat by sliding friction
Section 3
(19 cards)