Physics Homework Chapter 14

Follow me on Twitter @MikeBirkhead1
LMK what classes you're taking over the summer and next fall. If I can help, I will.
Videos will be posted on Friday and Saturday.

1. Earthquakes at fault lines in Earth's crust create seismic waves, which are longitudinal (P-waves) or transverse (S-waves). The P-waves have a speed of about 5 km/s. Estimate the average bulk modulus of Earth's crust given that the density of rock is about 2,700 kg/m³.
_____ Pa






2. On a hot summer day, the temperature of air in Arizona reaches 101°F. What is the speed of sound in air at this temperature? (Enter your answer to four significant figures. The speed of sound at 0°C is 331 m/s. use the conversion 0°C = 273 K as necessary.)
_____ m/s






3. A group of hikers hears an echo 2.10 s after shouting. how far away is the mountain that reflected the sound wave? (Assume the speed of sound is 340.6 m/s.)
_____ m







4. The range of human hearing extends from approximately 20 Hz to 20,000 Hz. Find the wavelengths of these extremes at a temperature of 11°C.
20 Hz        _____ m
20,000 Hz _____ m







5. When at res, two trains have sirens that emit a frequency of 300 Hz. The trains travel toward one another and toward an observer stationed between them. One of the trains moves at 32.5 m/s, and the observer hears a beat frequency of 2.9 beats per second. What is the speed of the second train, which travels faster than 32.5 m/s?
_____ m/s






6. Two trains on separate tracks move toward each other. Train 1 has a speed of 137 km/h; train 2 a speed of 77.0 km/h. Train 2 blows its horn, emitting a frequency of 500 Hz. What is the frequency heard by the engineer on train 1?
_____ Hz






7. At rest, a car's horn sounds the note A (440 Hz). The horn is sounded while the car is moving down the street. A bicyclist moving in the same direction with one-third the car's speed hears a frequency of 413 Hz.

a) Is the cyclist ahead of or behind the car?
_____

b) What is the speed of the car?
_____ m/s








8. An alert physics student stands beside the tracks as a train rolls slowly past. He notes that the frequency of the train whistle is 490 hz when the train is approaching him and 471 Hz when the train is receding form him. Using these frequencies, he calculates the speed of the train. What value does he find?
_____ m/s






9. A steel wire in a piano has a length of 0.7000 m and a mass of 3.900 x 10^-3 kg. To what tension must this wire be stretched so that the fundamental vibration corresponds to middle C (ƒ_c = 261.6 Hz on the chromatic musical scale)?
_____ N






10. A stretched string of length L is observed to vibrate in six equal segments when driven by a 637-Hz oscillator. What oscillator frequency will set up a standing wave so that the string vibrates in three segments?
_____ Hz






11. A steel wire with mass 27 g and length 1.15 m is strung on a bass so that the distance from the nut to the bridge is 1.10 m.

a) Compute the linear density of the string.
_____ kg/m

b) What velocity wave on the string will produce the desired fundamental frequency of the E₁ string, 45.23 Hz?
_____ m/s

c) Calculate the tension required to obtain the proper frequency.
_____ N

d) Calculate the wavelength of the string's vibration.
_____ m

e) What is the wavelength of the sound produced in air? (Assume the speed of sound in air is 343 m/s.)
_____ m






12. The windpipe of a typical whooping crane is about 5.1 ft long. What is the lowest resonant frequency of this pipe, assuming that it is closed at one end? Assume a temperature of 35°C.
_____ Hz






13. The human ear canal is about 2.4 cm long. If it is regarded as a tube open at one end and closed at the eardrum, what is the fundamental frequency around which we would expect hearing to be most sensitive?
_____ kHz






14. A pipe open at both ends has a fundamental frequency of 320 Hz when the temperature is 0°C.
a) What is the length of the pipe?
_____ m

b) What is the fundamental frequency at a temperature of 30°C?
_____ Hz






15. Two train whistles have identical frequencies of 1.47 x 10² Hz. When one train is at rest in the station and the other is moving nearby, a commuter standing on the station platform hears beats with a frequency of 8.00 beats/s when the whistles operate together. What are the two possible speeds that the moving train can have?
_____ m/s moving towards the station
_____ m/s moving away from the station

Physics Homework Ch 13

1. A block of mass m = 0.55 kg is attached to a spring with a force constant 109 N/m is free to move on a frictionless, horizontal surface as in the figure below. The block is released from rest after the spring is stretched at distance A = 0.13 m. (Indicate the direction with the sign of your answer. Assume that the positive direction is to the right).

a) At that instant, find the force on the block.
______ N

b) At that instant, find its acceleration
______ m/s²





2.The force constant of a spring is 165 N/m.

a) Find the magnitude of the force required to compress the spring by 4.20 cm from its unstretched length.
______ N

b) Find the magnitude of the force required to stretch the spring by 7.96 cm from its unstretched length.
______ N





3. A slingshot consists of a light leather cup containing a stone. The cup is pulled back against two parallel rubber bands. It takes a force of 15 N to stretch either one of these bands 1.0 cm.

a) What is the potential energy stored in the two bands together when a 44-g stone is placed in the cup and pulled back 0.11-m from the equilibrium position?
______ J

b) With what speed does the stone leave the slingshot?
______ m/s






4. A 10.0-g bullet is fired into, and embeds itself in, a 1.95-kg block attached to a spring with a force constant of 16.2 N/m and whose mass is negligible. How far is the spring compressed if the bullet has a speed of 300 m/s just before it strikes the block and the block slides on a frictionless surface? Note: You must use conservation of momentum in this problem because of the inelastic collision between the bullet and block.
______ m





5. A man enters a tall tower, needing to know its height. He notes that a long pendulum extends from the ceiling almost to the floor and that its period is 10.5 s.

a) How tall is the tower?
______ m

b) If this pendulum is taken to the moon, where the free-fall acceleration is 1.67 m/s², what is the period there?
______ s






6. 10.03 A simple pendulum has a lenght of 52.1 cm and makes 83.8 complete oscillations in 2.00 min.

a) Find the period of the pendulum.
______ s

b) Find the value of g at the location of the pendulum.
______ m/s²






7. The sunusoidal wave shown in the figure below is traveling in the positive x-direction and has a frequency of 14.5 Hz.

a) Find the amplitude.
_____ cm

b) Find the wavelength.
______ cm

c) Find the period
______ s

d) Find the speed of the wave
______ m/s





8. Light waves are electromagnetic waves that travel at 3.00 x 10⁸ m/s. The eye is most sensitive to light having a wavelength of 5.50 x 10⁷ m.

a) Find the frequency of this light wave.
_______ Hz

b) Find its period
_______ s

9. A circus performer stretches a tightrope between two towers. He strikes one end of the rope and sends a wave along it toward the other tower. He notes that it takes the wave 0.885 s to reach the opposite tower, 20.0 m away. If a 1.00-m length of rope has a mass of 0.360 kg, find the tension in the tightrope.
______ N

10. A piano string having a mass per unit length equal to 4.80 x 10^-3 kg/m is under a tension of 1,450 N. Find the speed with which a wave travelson this spring.
______ m/s

ExplainEverything App better than the competition

About two months ago I switched from using educreations to using ExlpainEverything to create the videos found on this blog. Recently, Mike's Online Biology blog was featured on the Explain Everything Website.

I wanted to take a few minutes to explain why I switched from Educreation (a very easy to use and simple App) to using ExplainEverything.

I first started tinkering with the thought of using a whiteboard screencasting app when I saw what Sal Khan was doing with Khan Academy. Khan Academy boasts the most comprehensive (free) online college-level education and even has math tutorials starting from counting and going up through Calculus. I found out about Khan academy while finishing the last semester of my Associates Degree. I was only a little perturbed because I had tried in vain to find a great way to learn biology while I was in Iraq and not once did a Google search return Khan Academy in my search results.

While in Iraq, I had decided to get out of the military and go back to school, with the hope of becoming a doctor. I had a year to get a jump start on my education, but I had no educators or books to learn from. I watched as much as I could find on YouTube  which was a scant few videos covering topics in the central dogma (DNA - RNA - Protein).

After seeing the Khan videos, I thought that this exact same process should be done for every class a college offers. At that point, I thought I would do my part. I sought out an app that would record me while I taught. I found educreations. It's a great app, but I'd like to list the pros and cons

Educreation Pros:
-Very easy to use (start making videos within minutes of downloading)
-Fast processing and uploading of videos to an online server (literally within 2 minutes most of the time)
-Image search feature which allows images to be imported directly from a bing search (I prefer google images).
-an undo button that always works exactly as expected

Educreation Cons:
-Cannot edit the timeline when a mistake is made
-Cannot save template set-ups (if you want to start over you retype everything and redownload all images, and rework EVERYTHING)
- Very poor sound quality (I had to yell in order to record at normal conversational volume)
- CANNOT manage your videos post production

The last one is the most important to me. I cannot download my videos from educreation. They are stuck on the very unheard-of educreation server. I cannot upload them to youtube, I cannot edit them, and I cannot post advertisement overlays on them.

I have petitioned Educreations several times to enable downloading and they have always promised that it "might" be available in the future. Well, that promise is about a year old and nothing has changed. Now, I'm going through the long process of screen-capturing all of the videos I've uploaded and then formatting them to youtube format (A very tedious process).

Explain everything reverses the list:
ExplainEverything Pros:
- Edit the timeline and cut out mistakes
- Save templates for later use
- Better sound quality (no more yelling)
- insert, not only images, but also videos, Audio files, etc
- Allows upload to several different servers (youtube, dropbox, google drive, or even to your ipad photo library)

ExplainEverything Cons:
- the conversion time is about 15 minutes long and
- you can't do anything on your ipad during conversion or it starts over.
      NOTE: if you have a mac or macbook
                 then the mac will do the compression on the computer and free up your ipad
                  No compressor is available for standard PC.
- Takes about an hour or two to get a good understanding of all of the features and how to best use them
- Still haven't figured out the "undo" button. It certainly doesn't work while I'm recording.

Overall, though, the Cons of ExplainEverything are far outweighed by the Pros. I recommend ExplainEverything, not because I was featured on their site, but because they have a great app that I enjoy using.

Physics Homework Ch 12

1. An ideal gas is enclosed in a cylinder with a movable piston on top of it. The piston has a mass of 8,000 g and an area of 5.00 cm² and is free to slide up and down, keeping the pressure of the gas constant.

a) How much work is done on the gas as the temperature of 0.155 mol of the gas is raised from 30.0° to 340°C?
______ J

b) What does the sign of your answer to part (a) indicate?
- the gas does positive work on its surroundings
- there is no work done, by the gas or the surroundings
- The surroundings do positive work on the gas





2. Gas in a container is at a pressure of 1.8 atm and the volume of 9.0 m³.

a) What is the work done on the gas if it expands at constant pressure to twice its initial volume?
_____ J

b) What is the work done on the gas if it is compressed at constant pressure to one quarter of its initial volume?
______ J



3.A gas expands from I to F along the three paths indicated in the figure below. Calculate the work done on the gas along each of the following paths.

a) IAF
______ J
b) IF
______ J
c) IBF
______ J





4. One mole of an ideal gas initially at a temperature of T_i = 1.8°C undergoes an expansion at a constant pressure of 1.00 atm to three times its original volume

a) Calculate the new temperature T_f of the gas.
______ K

b) Calculate the work done on the gas during the expansion.
_____ kJ





5. One mole of an ideal gas initially at a temperature of 1.50 x 10²°C is compressed at a constant pressure of 2.00 atm to two-thirds its initial volume.

a) What is the final temperature of the gas?
_____ K

b) Calculate the work done on the gas during the compression.
_____ J






6. An ideal gas in a cylinder is compressed very slowly to one-third its original volume while its temperature is held constant. The work required to accomplish this task is 64 J.

a) What is the change in the internal energy of the gas?
_____ J

b) How much energy is transferred to the gas by heat in this process?
_____ J




7. A gas is compressed at a constant pressure of 0.800 atm from 9.00 L to 2.00 L. In the process, 390 J of energy leaves the gas by heat.

a) What is the work done on the gas?
_____ J

b) What is the change in its internal energy?
_____ J




8. Five moles of gas initially at a pressure of 2.00 atm and a volume of 0.300 L has internal energy equal to 82.0 J. In its final state, the gas is at a pressure of 1.50 atm and a volume of 0.800 L, and its internal energy equals 168 J.

a) For the paths IAF, IBF, and IF in the figure above, calculate the work done on the gas.
W_IAF = ______ J
W_IBF = ______ J
W_IF = ______ J

b) For the paths IAF, IBF, and IF in the figure above, calculate the net energy transferred to the gas by heat in the process.
Q_IAF = _____ J
Q_IBF = _____ J
Q_IF = _____ J





9. A heat engine operates between a reservoir at 24°C and one at 439°C. What is the maximum efficiency possible for this engine?
______





10.In each cycle of its operation, a heat engine expels 3,000 J of energy and performs 1,700 J of mechanical work.

a) How much thermal energy must be added to the engine in each cycle
______ J

b) Find the thermal efficiency of the engine.
_____ %




11. One of the most efficient engines ever built is a coal-fired steam turbine engine in the ohio valley, driving an electric generator as it operates between 1870°C and 430°C.

a) What is its maximum theoretical efficiency?
______ %

b) Its actual efficiency is 42.0%. How much mechanical power does the engine deliver if it absorbs 1.8 x 10⁵ J of energy each second from the hot reservoir?
_____ kW





12. An engine absorbs 1.68 kJ from a hot reservoir at 277°C and expels 1.16 kJ to a cold reservoir at 27°C in each cycle.

a) What is the engine's efficiency?
______ %

b) How much work is done by the engine in each cycle?
______ J

c) What is the power output of the engine if each cycle lasts 0.305 s?
______ kW





13. A heat pump has a coefficient of performance of 3.75 and operates with a power consumption of 6.90 x10³ W.

a) How much energy does it deliver into a home during 6 h of continuous operation?
______ J

b) How much energy does it extract from the outside air?
______ J




14. A heat engine operates in a Carnot cycle between 82.0°C and 340°C. It absorbs 21,600 J of energy per cycle from the hot reservoir. The duration of each cycle is 4.00 s.

a) What is the mechanical power output of this engine?
_____ kW

b) How much energy does it expel in each cycle by heat?
______ kJ

Physics Homework Ch 11

Did anyone have a "Hardest Question"?
Let's all say what our hardest questions were in the comments... I think it will help us study for the exam, He doesn't tend to pick the longest questions, but does like the "hardest questions"
Post below!

NOTE: Chart for specific Heat and Latent Heat at bottom of page

1. The temperature of a gold bar rises by 10.0°C when it absorbs 0.677 kJ of energy by heat. THe mass of the bar is 525 g. Determine the specific heat of gold from these data.
_______ kJ/kg · °C




(Don't forget to click "like")

2. Lake Erie contains roughly 4.00 x 10¹¹ m³ of water.

a) How much energy is required to raise the temperature of that volume of water from 11.0°C to 14.0°C?
______ J

b) How many years would it take to supply this amount of energy by using the 850-MW exhaust energy of an electric power plant?
_____ yr


(Don't forget to click "like")


3. A certain steel railroad is 13 yd in lenght and weighs 56.3 lb/yd. How much thermal energy is required to increase the length of such a rail by 3.0 mm? Note: Assume the steel has the same specific heat as iron.
______ J
NOTE: Click here for Coefficient of Thermal Expansion Chart


(Don't forget to click "like")


4. What mass of water at 27°C must be allowed to come to thermal equilibrium with a 1.86-kg cube of aluminum initially at 1.50 x 10²°C to lower the temperature of the aluminum to 59.3°C? Assume any water turned to steam subsequently recondenses.
_______ kg


(Don't forget to click "like")


5. An aluminum cup contains 225 g of water and a 40-g copper stirrer, all at 27°C. A 420-g sample of silver at an initial temperature of 87°C is placed in the water. The stirrer is used to stir the mixture gently until it reaches its final equilibrium temperature of 32°C. Calculate the mass of the aluminum cup.
______ g


(Don't forget to click "like")


6. A 100 g aluminum calorimeter contains 250 g of water. The two substances are in thermal equilibrium at 10°C. Two metallic blocks are placed in the water. One is a 50 g piece of copper at 76°C.  The other sample has a mass of 68 g and is originally at a temperature of 100°C. The entire system stabilizes at a final temperature of 20°C. Determine the specific heat of the unknown second sample.
_______ J/kg·°C


(Don't forget to click "like")


7. A student drops two metallic objects into a 120-g steel container holding 150 g of water at 25°C. One object is a 160-g cube of copper that is initially at 75°C, and the other is a chunk of aluminum that is initially at 5.0°C. To the surprise of the student, the water reaches a final temperature of 25°C, precisely where it started. What is the mass of the aluminum chunk?
_______ g


(Don't forget to click "like")


8. A 90-g ice cube at 0°C is placed in 910 g of water at 22°C. What is the final temperature of the mixture?
______ °C


(Don't forget to click "like")


9. A 74-g ice cube at 0°C is heated until 66g has become water at 100°C and 8.0g has become steam at 100°C. How much energy was added to accomplish the transformation?
______ J


(Don't forget to click "like")


10. A 40- g block of ice is cooled to -76°C and is then added to 600 g of water in a 80-g copper calorimeter at a temperature of 27°C. Determine the final temperature of the system consisting of the ice, water, and calorimeter. (If not all the ice metls, determine how much ice is left.) Remember that the ice must first warm to 0°C, melt, and then continue warming as water. (The specific heat of ice is 0.500 cal/g · °C = 2,090 J/kg · °C.)
T_f  = ______ °C
m_{ice final} = ______g

(Don't forget to click "like")


11. A glass windowpane in a home is 0.62 cm thick and has dimensions of 1.14 m x 1.78 m. On a certain day, the indoor temperature is 26°C and the outdoor temperature is 0°C. (Assume the thermal conductivity of the glass is 0.8 J/s · m · °C.)

a) What is the rate at which energy is transferred by heat through the glass?
______ W

b) How much energy is lost through the window in one day, assuming the temperatures inside and outside remain constant?
______ J

 
(Don't forget to click "like")


12. A styrofoam box has a surface area of 0.79 m² and a wall thickness of 2.0 cm. The temperature of the inner surface is 5.0°C, and the outside temperature is 26°C. If it takes 8.5 h for 5.0 kg of ice to melt in the container, determine the thermal conductivity of the styrofoam.
______ W/m · K

(Don't forget to click "like")

Specific Heats at atmospheric pressure:

Substance	J/kg ∙ °C	Cal/g ∙ °C
Aluminum	900	0.215
Beryllium	1820	0.436
Cadmium	230	0.055
Copper	387	0.0924
Ethyl Alcohol	2430	0.581
Germainium	322	0.077
Glass	837	0.200
Gold	129	0.0308
Human tissue	3470	0.829
Ice	2090	0.500
Iron	448	0.107
Lead	128	0.0305
Mercury	138	0.033
Silicon	703	0.168
Silver	234	0.056
Steam	2010	0.480
Tin	227	0.0542
Water	4186	1.00
Ice (H2O)	2090	0.500

Latent Heats of Fusion and Vaporization for some materials

Substance	Melting point (°C)	Latent Heat Fusion    (J/kg)	Boiling Point  (°C)	Latent Heat Vaporization (J/kg)
Helium	-269.65	5.23 x 103	-268.93	2.09 x 104
Nitrogen	-209.97	2.55 x 104	-195.81	2.01 x 105
Oxygen	-218.79	1.38 x 104	-182.97	2.13 x 105
Ethyl alcohol	-114	1.04 x 105	78	8.54 x 105
Water	0.00	3.33 x 105	100.00	2.26 x 106
Sulfur	119	3.81 x 104	444.60	3.26 x 105
Lead	327.3	2.45 x 104	1750	8.70 x 105
Aluminum	660	3.97 x 105	2450	1.14 x 107
Silver	960.80	8.82 x 104	2193	2.33 x 106
Gold	1063.00	6.44 x 104	2660	1.58 x 106
Copper	1083	1.34 x 105	1187	5.06 x 106