Physics 3 – Sept 1, 2016
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Do Now: P3 Challenge – (Answers only on paper – report energies in kJ )
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A 60 kg bungee jumper jumps from a bridge. She is tied to a 12 m long bungee cord and falls a total
of 31 m.
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a) How much gravitational potential energy does she have before jumping. (Set the origin of your
frame of ref at the bottom of her fall.)
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b) How much kinetic energy does she have when she stops freefalling and the bungee is not yet
stretching?
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c) What velocity does she have when the bungee starts to stretch?
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d) How much energy is absorbed by the bungee and stored as spring potential energy?
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e) What is the spring constant, k, of the bungee cord?
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f) How much work does gravity do on the girl during the jump?
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g) How much work does the bungee cord do on the girl during the jump?
Objectives/Agenda
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Objective: Work and Energy
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Agenda:
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P3 question to review kinetic energy, gravitational potential energy, spring
potential energy, conservation of energy, work-kinetic energy theorem,
calculation of work
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Additional problem solving to practice.
Assignment: Prepare for Unit 3-5 Mastery Quizzes Next week
About Work and Energy
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Sign convention: + work on a system adds energy to the system
- work on a system removes energy from the system
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Work kinetic energy theorem: Wnet = ∆K
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Conservation of mechanical Energy only applies if only conservative
forces are present. (Gravity, spring, electrical etc…)
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uses the NET work
Nonconservative forces: friction, air resistance, etc…
For every conservative force, there is a corresponding potential energy.
Topics Reviewed Sept 1
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Bungee jumper combination of gravitational and spring potential energies
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Work on an incline, with and without friction
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Kinetic energy of an oxygen molecule
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Work done to catch a baseball
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Energy considerations for a pole vaulter, a high jumper and a trampoline artist
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Energy of a mass on a vertical spring.
Today’s Assignment
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Continue reviewing 2.2, 2.3, 2.4
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Prepare for Unit 3-5 Mastery Quizzes Next week
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Mastery quizzes are worth 10 points and will be two multiple choice
questions with 8 points of problems. (Usually one or two problems).
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IB materials will be integrated as much as possible.
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May retake mastery quizzes as needed to reach 8/10 proficiency level.
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See me during Lunch or after school. Schedule your retakes and give me
at least 24 hours to prepare the quiz for you