Physics 207: Lecture 15, Pg 1Physics 207, Physics 207, Lecture 15, OctLecture 15, Oct 26 26 ‘‘0909TODAY:TODAY:Rigid Body Rotation (Chapter 12)Rigid Body Rotation (Chapter 12)Review Angular Rotation, Velocity, Acceleration: Θ, ω, α• Center of Mass: (xcm,ycm)• Moment of Inertia: I• Kinetic Energy of Rotation• End of topics on Exam 2• Angular Momentum• Torque• StaticsASSIGNMENTS:ASSIGNMENTS:Exam 2 Practice Problems on MPExam 2 Practice Problems on MPSolutions available at librarySolutions available at library reserve sitereserve siteExam 2 Exam 2 thurs thurs night 5:45night 5:45 -7:00-7:00-- note new venuenote new venue- topics- topics through Chapter 12.4through Chapter 12.4Physics 207: Lecture 15, Pg 2Human Energy NeedsHuman Energy NeedsThrough the AgesThrough the AgesHunter-Gatherers (no domestic animals):Work done/day:50 W for 12 hours/day ~ 2 MJTotal daily per capita energy used:(work + metabolic) ~ 3000 kCal/day ~ 13 MJAverage power use: ~ 150 WPhysics 207: Lecture 15, Pg 3Human Energy NeedsHuman Energy NeedsThrough the AgesThrough the AgesAgrarian societies (1 domestic animal per 2 people):Work done/day:300 W (~0.4 hp) for 12 hours/day ~ 13 MJTotal daily per capita energy used:(work + metabolic) ~ 20 kCal/day ~ 80 MJAverage power use: ~ 900 WPhysics 207: Lecture 15, Pg 4Human Energy NeedsHuman Energy NeedsThrough the AgesThrough the AgesModern Industrial Societies (e.g. US):Total daily per capita energy used: ~ 720 MJ(excludes food energy)Average power use: ~ 8.4 kW~ 50 lbs of oil/day or ~ 11 hpPhysics 207: Lecture 15, Pg 5Physics 207: Lecture 15, Pg 6Physics 207: Lecture 15, Pg 8Physics 207: Lecture 15, Pg 9Rotational EnergyRotational Energy About how much energy is stored in a flywheel that is 1 m indiameter, has a mass of 100 kg, and is spinning at 30revolutions/sec?A. 200 J B. 2000 J C. 20,000 J D. 200,000 J How long would this power a car using 100 hp ?(1 hp = 746 W)Physics 207: Lecture 15, Pg 10Physics 207: Lecture 15, Pg
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