Fundamentals of Physics Exam 3
Heat transfer P=
(area * temp difference * thermal conductivity) / thickness
pressure and liquid depth
+1 atm for every 10m/ 33ft
actual pressure from a pressure gauge?
Pressure read in a pressure gauge does not include atmospheric pressure- the actual pressure you have to add 1 atm (14.7 PSI)
If heat flows into a system, ________. a. the system will be able to do more work b. the system will be able to do less work c. the work capacity of the gas is not affected
a
Bernoulli's Principle states that, as the velocity of a fluid increases, ________. a. the temperature of the fluid will also increase b. the volume of the fluid will decrease c. the pressure in the fluid will decrease d. the pressure in the fluid will also increase
c
Clouds and fog are caused by ________. a. evaporating liquid water b. burning too many fossil fuels c. condensing water vapor d. vapor deposition in the atmosphere
c
Compared to an increase in temperature of 20 Fahrenheit degrees, an increase in temperature of 20 Celsius degrees is ________. a. the same b. smaller c. larger
c
If the pressure in a gas is multiplied by a factor of 6 and the temperature is multiplied by a factor of 3, the volume of the gas will be ________ the original volume. a. three times b. twice c. one half of d. one third of
c
In a plasma, the ________. a. atoms are broken down into molecules b. protons are separated from the neutrons c. electrons are separated from the nuclei d. isotopes are separated by charge
c
In a standard refrigerator, it is the ________ that is most responsible for the transfer of heat. a. latent heat of refrigeration b. latent heat of fusion c. latent heat of vaporization d. latent heat of sublimation
c
Truck A comes to a stop from 20 m/s by crashing into a haystack. Truck B comes to a stop from 20 m/s by crashing into a brick wall. Both trucks have the same mass. Compared to truck A, the impulse on truck B during the collision is ________. a. larger b. more concentrated c. the same d. smaller
c
When a boat is floating in the water, ________. a. the buoyant force is greater than the weight of the boat b. the buoyant force equals the mass of the boat c. the buoyant force equals the weight of the boat d. the volume of displaced water equals the volume of the boat
c
You drop a blob of clay and a golf ball of equal mass onto a hard surface. The clay sticks to the surface, while the golf ball bounces. Compared to the impulse on the clay, the impulse on the golf ball is ________. a. smaller b. zero because the forces cancel out c. larger d. the same
c
Hooke's Law
the amount of stretch or compression of an elastic material is directly proportional to the applied force: f~Δ(x) k = spring constant F= kΔx F (N) force x (m) length it changes k (n/m) constant how easy it is to stretch and compress ex. im 70 kg i sit on a spring it compresses 2cm. Constant? weight= (70kg)(10m/s) 2cm= .02m F=kx 700N=k(.02m) = 35,000 N/m
The primary energy source of the Earth is ________. fossil fuels geothermal energy radioactive elements in the core the sun
the sun
surface tension
the tendency of the surface of a liquid to contract in area and thus to behave like a stretched elastic membrane
internal energy
the total of all molecular energies, kinetic plus potential, that are internal to a substance.
Normal room temperature is closest to ________.
300 Kelvin, 20-22 C, 68- 72 F
Absolute zero is approximately ________
-273 Celsius, 0 Kelvin, -459.67 Fahrenheit the lowest possible temperature that a substance may have- their temperature at which molecules of the substance have their minimum kinetic energy. no more energy can be extracted, cannot be cooler
solar constant
1400 J/m2 received from the sun each second at the rop of Earth's atmosphere on an area perpendicular to the sun's rays; expressed in terms of power, 1.4 kW/m2
If you triple the diameter of a ball, the volume of the ball will be:
27x larger
A 100 kg student carrying 25 kg of pumpkins runs up a 10 m high flight of stairs in 20 seconds. The average power exerted by the students during this time is ________. Correct! 625 W 125 W 1250 W 12.5 kW
625 W
Earth's atmosphere is composed primarily of ________.
78% Nitrogen 21% O 9% Ar .04% CO2
EM spectrum
> low freq/ long wavelength radio micro infrared ROYGBIV ultraviolet X gamma < high freq/ shorter wavelength
Do all materials expand when heated?
No. One example is water
ideal gas law
PV=nRT P= pressure (atm) OR Pa V= L OR m3 n= # moles of particles OR # particles, not moles R= universal gas constant OR 1.38 * 10^23 J/K T= temp (K) PV/NT=K (x2)(x3)/(x2)(?) = x3- must keep constants
If the linear dimensions of an object are doubled, by how much does the surface area increase? By how much does the volume increase? (scaling)
SA increases by 4, volume increases by 8
Why can small creatures fall considerable distances without injury while people need parachutes to do the same?
Small creatures have a larger surface area relative to body weight, and they encounter greater air resistance relative to body weight, resulting in a slower fall than that of larger creatures
humidity
The amount of water vapor in the air
What/ where is the neutral layer in a beam that supports a load?
The region of neither tension nor compression when supporting a load; the middle portion of the beam.
If you have two differently-sized spheres of metal and they have the same mass, then ________. a. The smaller sphere is denser b. Their densities are proportional to their sizes c. The larger sphere is denser d. They have the same density as well
a
principle of flotation
a floating object displaces a weight of fluid equal to its own weight
temperature
a measure of the average translational kinetic energy per molecule in a substance.
plasma
an electrified gas that contains ions and free electrons. most of the matter in the universe is in the plasma phase; electrons and nuclei are separated; Most plasmas are created when extra energy is added to a gas, knocking electrons free from atoms. High temperatures often cause plasmas to form. Atoms in a hot gas are moving so fast that when they collide with each other they sometimes knock electrons loose.
archimedes priciple
an immersed body is buoyed up by a force equal to the weight of the fluid it displaces; m helium balloon ascending- if free to expand as it rises, it will increase vol and decrease density to keep rising- they usually expand a little then settle where the buoyancy matcher the weight
Archimedes principle (air)
an object in the air is buoyed up with a force equal to the weight of the displaced air
scaling
as an object gets larger, it has less surgace area compared to volume; chipmunk has more skin area per lb than an elephant; more surface area = can react w surroundings better; 2x length= 4x surface area= 8x vol and weight
A material with a low specific heat will tend to ________. a. cool down quickly but heat up slowly b. heat up and cool down quickly c. heat up quickly but cool down slowly d. heat up and cool down slowly
b
A moving 5000-kg freight car collides with a 10,000-kg freight car at rest. They couple upon collision and move at 2 m/s. What was the initial speed of the 5000-kg car? a. 9 m/s b. 6 m/s c. 5 m/s d. 15 m/s
b
Arches work well in construction because ________. a. The entire structure is under tension b. The entire structure is under compression c. The compression and tension balance each other out.
b
Automobile safety devices like padded dashboards and airbags work by ________. a. decrease average impulse by distributing it over a larger distance b. decreasing average force by extending the time of the collision c. decreasing average force by shortening the time of the collision d. decreasing the change in momentum involved
b
Compared to smaller animals, larger animals have a ________. a. similar ratio of surface area to weight b. smaller ratio of surface area to weight c. larger ratio of surface area to weight d. The pressure under 100 feet of salt water is closest to ________.
b
If a tire pressure gauge reads 30 PSI, the actual absolute pressure in the tire is closest to ________. a. 150 kPa b. 45 PSI c. 90 mmHg d. 15 PSI
b
In a hydraulic press (hydraulic lever), if the force is multiplied by a factor of 20, ________. a. the pressure is also multiplied by a factor of 20 b. the distance is divided by a factor of 20 c. the distance is also multiplied by a factor of 20 d. the product of force x distance is also multiplied by 20
b
In a pressure cooker, the food is cooked faster than in a normal pot because ________. a. the increased pressure breaks down the food molecules faster b. the water boils at a higher temperature c. the lower pressure breaks down the food molecules faster d. the water boils at a lower temperature
b
When a gas is compressed, ________. a. its internal energy will decrease b. its internal energy will increase c. the gas will expand d. internal energy will flow out of the gas
b
Compared to a cup of hot coffee, a bathtub full of lukewarm water has ________. a. lower internal energy and lower average molecular energy b. higher average molecular energy but lower internal energy c. higher internal energy but lower average molecular energy d. higher internal energy and higher average molecular energy
c internal energy= sum of all energies- bigger = more- KE, PE, etc. molecular is heat energy, average speed of molecules
adiabatic process
compressing or expanding a gas while no heat enters or leaves the system insulate a system from its surroundings
In a standard air conditioner or heat pump, the refrigerant ________ outside and ________ inside.
condenses, evaporates
If a window is perfectly sealed (no air leaks), heat can still penetrate via ________.
conduction and EM radiation
.Pressure can be increased by ________. a. increasing the area or decreasing the force b. taking more time to relax c. raising both the force and the area by proportional amounts d. increasing the force or decreasing the area
d
A 1000 kg automobile is pushed a distance of 20 m with a force of 2500 N. The speed of the car at the end of the 20 m will be ________. a. 5 m/s b. 25 m/s c. 40 m/s d. 10 m/s
d
A 1000 kg automobile is pushed a distance of 20 m with a force of 2500 N. The work done on the automobile is ________. a. 50 MJ b. 200 kJ c. 500 kJ d. 50 kJ
d
An elastic material is one that___. a. Keeps its new shape once deformed b. Bends at least somewhat before breaking c. Is relatively easy to deform. d. Returns to its original shape after being deformed.
d
Global warming due to the Greenhouse Effect ________ . a. was first discovered by Al Gore in the early 1970's b. is a Chinese hoax designed to take away our jobs c. may actually be due to ash and other contaminants from volcanos d. can happen on any planet with an atmosphere
d
The pressure under 100 ft of saltwater is closest to: a. 45 PSI b. 3 atm c. 20,000 leagues d. 400kPa
d
When water vapor condenses into liquid water, it ________. a. must pass through a solid phase b. transfers heat to the liquid water with no net heat flow to the environment c. absorbs heat from the environment d. releases heat to the environment
d
a cannon recoils while firing a cannonball. The speed of the cannon's recoil is relatively small because the ________. a. momentum is mainly concentrated in the cannonball b. force against the cannon is smaller than against the ball c. momentum of the cannon is smaller d. cannon has much more mass than the cannonball
d
Ninety nine percent of our atmosphere is contained in a layer about ________ thick. a. 30 miles b. 10 miles c. 40 miles d. 20 miles
d Density of atmosphere- KE of molecules= tend to disperse, while gravity pulls them down near earth
capillarity
the rise of a liquid in a fine, hollow tube or in a narrow space
solar power
energy per unit time received from the sun
Where do tension and compression occur?
for horizontal beams, compression at the top, tension at the bottom; stretched= tension, squashed= compression; vertical beams = compressed;
condensation
gas > liquid opposite of evap warming fast moving gas speeds up then collides w liquid and becomes part of it- shares KE w liquid
latent heat
heat absorbed or radiated during a change of phase at a constant temperature and pressure L=Q/M L=specific latent heat of a substance Q=energy released or absorbed during phase change m=mass
2nd law of thermodynamics
heat of itself never flows from a cold object to a hot object a cold object can do work on colder things, but not hotter
most biologically damaging waves?
higher freq shorter wavelength most penetrating
sublimation
ice> gas evaporation fast molecules evaporate while slow ones stay behind = cooling
I- beam use?
it is like a solid bar with some of the steel scooped from the middle, where it is needed the least. Beam is lighter but has the same strength.
evaporation
liquid > gas a cooling process- molecules cool as they drift away
The lower the temperature of an object, the ________ the wavelength of electromagnetic radiation it emits
longer
The longer the wavelength of electromagnetic radiation, the ________ the frequency.
lower higher frequency = shorter wavelength
density
mass of a substance per unit volume. d=m/v weight density = weight/v
amplitude = a
max deviation from equilibrium in the wave measured in diff units depending on type of wave larger amp= more energy / wave
barometer
measures atmospheric pressure
regelation
melt under pressure then freeze again at removal of temp
frequency ex. medical ultrasounds are usually 5 mHz. Period?
number of vibrations; we can hear frequencies of 20- 20,000 Hz 100 Hz= 100 vibes per sec period = time for one complete wave F=1/T T=1/F ex. T=1/f = 1/5*10^6 Hz = 200 * 10^9 s = 200 ns
Pressure under water
pressure at surface + pressure of water P= Po+pgh Po= pressure at surface 101.3kPa p= density of fluid (kg/m3) g= gravity = 10 m/s2 h= depth (m)
Brownian motion
random microscopic movement of atoms in liquid or gas- responsible for dispersion and atmospheric pressure
Velocity
speed of energy flow m/s v = f λ
heat
the energy that flows from a substance of higher temp to a substance of lower temp, usually measured in calories or joules
Heat is defined as ________.
the flow of energy from a higher temperature object to a lower temperature object
If you touch a wooden pencil and a metal pen that have both been sitting on your desk, the pen feels cooler because ________.
the metal is a better heat conductor than wood
buoyant force
the net upward force that a fluid exerts on an immersed object. Acts upward on an object due to greater pressure at greater depth. When an object floats, its buoyant force equals its weight- buoyant force equals both the weight of the object and the weight of the water it displaced; a floating object displaces a weight of fluid equal to its own weight; buoyancy makes a hot air balloon rise- hot air is less dense than the cool air around it
Pascal's principle
the pressure applied to a motionless fluid confined in a container is transmitted undiminished throughout the fluid; makes hydraulic lever work when force is multiplied while distance is divided
atmospheric pressure
the pressure exerted against bodies immersed in the atmosphere, It results from the weight of the air pressing down from above. At sea level. atmospheric pressure it about 101 kPa.
Boyle's Law
the product of pressure and vol is a constant for a given mass of confined gas, as long as the temperature remains unchanged P1V1=P2V2 P= 1/V pressure and volume inversely proportional double one = half the other
specific heat capacity
the quantity of heat per unit mass required to raise the temperature of a substance by 1 degree C Q = mc∆T Q = quantity of heat transferred heat energy (Joules, J) m = mass of a substance (kg) c = specific heat capacity (units J/kg∙K) ∆T = change in temperature (Kelvins, K) specific heat = quantity of heat/ gram degree C
terrestrial radiation
the radiation emitted by earth to outer space
newtons law of cooling
the rate of loss of heat from a warm object is proportional to the temperature difference between the object and its surroundings. Similarly for the gain of heat by a cool object.
pressure
the ratio of force to the area over which that force is distributed P=F/a = Pa; 1Pa= 1 N/m^2 at sea level 1 atm= 101,325 Pa= 101.3 kPa= 14.7 PSI = 760 mmHg = 29.9 inHg liquid pressure= weight density * depth
(electromagnetic) radiation
the transfer of energy by means of electromagnetic waves all objects give off em rad amount and freq depends on temp and color can determine temp by measuring em freq dark absorbs and gives off more heat the speed of EM waves in air is c = 3 x 108 m/s
conduction
the transfer of heat energy by molecular and electron collisions within a substance (especially a solid)
convection
the transfer of heat energy in a gas or liquid by means of currents in the heated fluid, the fluid moves, carrying energy with it.
heat engine
uses heat as input to produce work
boiling
vaporization that occurs on and below the surface of a liquid lower pressure (vacuum) = can boil and freeze at the same time
Greenhouse effect
warming of the lower atmosphere by short wavelength radiation from the sun that penetrates the atmosphere, is absorbed by earth, and is reradiated at longer wavelengths that cannot easily escape Earth's atmosphere.
1st law of thermodynamics
when heat flows to of from a system, the system gains or loses an amount of energy equal to the amount of heat transferred heat added to a system = increase internal energy and amount of work done by the system
temperature inversion
when upper region of atm is warmer than lower- if rising air is denser than upper layer of warm air, it won't rise
ideal efficiency
when work is done by a heat engine operating between 2 temps, Thot and Tcold, only some of the heat can be converted into work, the rest is expelled at Tcold ideal efficiency = (Thot - Tcold) / Thot
Bernoulli's principle
where the speed of a fluid increases, the internal pressure in the fluid decreases; for airplanes- the wind design causes air to flow faster over the top and slower underneath, causing the high under pressure to lift it; higher pressure inside house causes the roof to blow off in a storm; higher velocity > lower pressure