Judah Levine, 3070L8 1http://physics.colorado.edu/phys3070http://physics.colorado.edu/phys3070Judah LevineJudah LevineJILA SJILA [email protected]@colorado.edu303 492303 492--7785 (27785 (2--7785)7785)M,F 11M,F 11--Noon, W 1Noon, W 1--3 pm3 pmalso by appointmentalso by appointmentJudah Levine, 3070L8 2AnnouncementsAnnouncementsQQFirst deadline for term paper is next First deadline for term paper is next FridayFridayQQGuest Lecturer next Wed and Fri: Prof. Guest Lecturer next Wed and Fri: Prof. Albert Bartlett: exponential growthAlbert Bartlett: exponential growthJudah Levine, 3070L8 3CAPA Assignment 1 #1CAPA Assignment 1 #1If you push a cart along a horizontal surface with a force of 21.0 pounds, and the cart moves 8.0 feet, how much work have you done in Joules?Judah Levine, 3070L8 4CAPA Assignment 1 #1CAPA Assignment 1 #1If you push a cart along a horizontal surface with a force of 21.0 pounds, and the cart moves 8.0 feet, how much work have you done in Joules? The work done is the force times the distance, or 8×21= 168 foot-pounds. From the front cover, 1 foot-pound is equal to 1.36 joules. Therefore the work in joules is 168 foot-pounds × 1.36 joules/foot-pounds = 228.5 jJudah Levine, 3070L8 5CAPA Assignment 1 #2CAPA Assignment 1 #2Your car has a mass of 1600 kg, and is traveling at a speed of 40 m/sec. What is its kinetic energy in BTU?Judah Levine, 3070L8 6CAPA Assignment 1 #2CAPA Assignment 1 #2Your car has a mass of 1600 kg, and is traveling at a speed of 40 m/sec. What is its kinetic energy in BTU?The kinetic energy is mv2/2 = 1600*402/2 =1.28×106joules. From the front cover 1 joule equals 9.49×10-4BTU. So1.28×106joules × 9.49×10-4BTU/1 joule = 1215 BTU = 1215Judah Levine, 3070L8 7Clicker QuestionClicker QuestionTaking the previous answer of 1215 BTU of kineticenergy, how much gasoline (in gallons) did it take to do this, assuming 100% efficiency?A: Less than 0.001B: About 0.01C: About 0.1D: About 0.5E: More than 0.5Judah Levine, 3070L8 8Clicker QuestionClicker QuestionTaking the previous answer of 1215 BTU of kineticEnergy, how much gasoline did it take to do this,Assuming 100% efficiency?ouncesgallonouncesgallongallonBTUgallonBTU25.1128107.9107.91025.111215335=×××=××−−B: About 0.01Judah Levine, 3070L8 9Clicker questionClicker questionHow fast is 40 m/sec?A: okay in a 20 mph school zoneB: okay in a 45 mph parkwayC: okay on a highway where limit is 55 mphD: okay on a highway where limit is 75 mphE: asking for a speeding ticket in all of theseJudah Levine, 3070L8 10Clicker questionClicker questionHow fast is 40 m/sec?Convert 40 m/sec to miles/hour:hourmilesfeetmilehourfeetmfeethrmhourm5.89528011072.4128.31044.11min60min1sec60sec4055=××=××=××E: asking for a speeding ticket in all of theseJudah Levine, 3070L8 11CAPA Assignment 1 #3CAPA Assignment 1 #3Per person, the energy consumption in the United States is about 4.1×108Btu/yr. Express this in Watts (W) Watts are joules/second, so lots of conversions:Judah Levine, 3070L8 12CAPA Assignment 1 #3CAPA Assignment 1 #3Per person, the energy consumption in the United States is about 4.1×108Btu/yr. Express this in Watts (W) Watts are joules/second, so lots of conversions:4.1×108Btu/yr × 1 year/365 days × 1 day/24 hours ×1 hour/60 minutes × 1 minute/60 seconds = 13 BTU/second × 1 joule/9.49×10-4= 1.37×104Judah Levine, 3070L8 13CAPA Assignment 2 #1CAPA Assignment 2 #1A windmill produces 1400 watts of electrical power that is used to heat water. The efficiency is 100%. How long will it take to raise the temperature of 20 gallons of water by 30 degrees FJudah Levine, 3070L8 14CAPA Assignment 2 #1CAPA Assignment 2 #1A windmill produces 1400 watts of electrical power that is used to heat water. The efficiency is 100%. How long will it take to raise the temperature of 20 gallons of water by 30 degrees FFirst convert to a consistent set. Since the problem uses British units for the water, we can convert the watts to the equivalent British unit. 1 watt = 1 joule/second (by definition), and 1 joule= 9.49×10-4BTU:1400 watts = 1400 joule/second= 1400 joule/second * 9.49×10-4BTU/joule= 1.3286 BTU/secondJudah Levine, 3070L8 15CAPA Assignment 2 #1CAPA Assignment 2 #1--concon’’tt1 gallon of water weighs about 8 pounds, so 20 gallons is 160 pounds of water. Since 1 BTU will raise 1 pound of water by 1F, 160 BTU are needed to raise all of the water by 1F, and 30×160=4800 BTU are needed to heat all of the water by the specified temperaturedifference. The time needed to do this is the number of BTUs divided by the rate or 4800/1.3286=3612.8 secondsJudah Levine, 3070L8 16Variation on a theme of heatingVariation on a theme of heatingSuppose the previous problem was the same except thatThe efficiency was 70% instead of 100%. How does that Change the answer?efficiencyoutputusefulinputinputefficiencyoutputusefulinputoutputusefulefficiency=×==Judah Levine, 3070L8 17Variation on a theme of heatingVariation on a theme of heatingSuppose the previous problem was the same except thatThe efficiency was 70% instead of 100%. How does that Change the answer?Input power is still 1400 watts, but the efficiency is only70%, so that the actual energy available is 0.7×1400=980 watts.The rest of the problem is unchanged except that theEnergy input rate is 0.7× 1.3286= 0.93 BTU/secondSo that the time is 4800/0.93=5161.2 sJudah Levine, 3070L8 18Another variationAnother variationTake the previous values of input power= 1400 wattsAnd time= 5161s.If you bought the electricity at $0.10 per kWH, howmuch would you pay?Judah Levine, 3070L8 19Another variationAnother variationTake the previous values of input power= 1400 wattsAnd time= 5161s.If you bought the electricity at $0.10 per kWH, howmuch would you pay?dollarskWHdollarskWHhourwattskilowattswatts2.01.02min601sec60min11000151611400=×=××××Remember: you are paying for the input power of 1400 wattsJudah Levine, 3070L8 20CapaCapaAssignment 2 Assignment 2 ----#2#2Identify each of the following as E-Energy, P-Power, N-Neither. A) horsepower/day Neither -- This is power/time B) Watt/day Neither -- same reasonC) kcalorie EnergyD) joules*sec Neither -- Energy*timeE) joules/sec Power -- Energy/timeF) kilowatt*hour Energy -- Power*timeJudah Levine, 3070L8 21CAPA Assignment 2 #3CAPA Assignment 2 #3It has been estimated that a person can perform continuous manual
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