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Do Now. Materials Notebook Homework Pen/Pencil 1 ) Take Out Your Homework, Put on Corner of Desks 2) In Notebooks: What is Power ? -Write a sentence in response.
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Do Now Materials Notebook Homework Pen/Pencil 1) Take Out Your Homework, Put on Corner of Desks 2) In Notebooks: What is Power? -Write a sentence in response. 3) In Notebooks: When Mr. Van Houten bench presses large amounts of weight he often will do 500 J of work in just 4 seconds. How much power do I develop?
Objectives • SWBAT solve simple power problems. • SWBAT solve work-energy theorem problems.
Agenda • Introduction to New Material: Work – Energy Theorem • Practice • More Practice • Exit Ticket SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Work – Energy Theorem • So far our exploration of energy has been so exciting. • A box sits on a cliff, how much energy does it have? • A spring shoots a dart straight up into the air, what’s the change in energy? • Your moving in a car how much kinetic energy do you have? SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Work – Energy Theorem • We’ve been talking about the energy of objects that are in closed systems. • For example, one system might be a box in a warehouse. • We haven’t considered the external world that may affect the box. • The box has no energy if it sits there, but if I pick it up and put it on a shelf… SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Work – Energy Theorem • Through the process of doing work, energy can move between the external world and the system. • The direction of this energy transfer can go both ways. • External world system • I lift a weight off the ground and hold it above my head. • Or, system external world • A moving golf club hits a still golf ball. SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Work – Energy Theorem Weight is the system
Work – Energy Theorem • External world system • I lift a weight off the ground and hold it above my head. • W is positive • Mr. Van Houten picks a weight up off the ground by doing 50 J of work on the weight. How much energy does the weight now have?
Work – Energy Theorem • Or, system external world • A moving golf club hits a still golf ball. • W is negative • A 2 kg golf club is being swung at 4 m/s, when it collides with a golf ball. During the collision, the club does 5 kg of work on the ball. What is the final energy of the golf club equal to?
Work – Energy Theorem • The work-energy theorem states that when work is done on an object, the result is a change in kinetic energy. • The work-energy theorem can be represented by: • Think back to Mr. Van Houten lifting the weight. SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Work – Energy Theorem Weight is the system
Work – Energy Theorem • The relationship between work done and the change in energy that results was established by James Prescott Joule. • To honor him, a unit of energy is called a joule (J). SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Example Problem #1 • A 105-g hockey puck is sliding across the ice. A player exerts a constant 4.50-N force over a distance of 0.150 m. How much work does the player do on the puck? What is the change in puck’s energy? d F
Example Problem #1 • A 105-g hockey puck is sliding across the ice. A player exerts a constant 4.50-N force over a distance of 0.150 m. How much work does the player do on the puck? What is the change in puck’s energy?
Example Problem #1 • A 105-g hockey puck is sliding across the ice. A player exerts a constant 4.50-N force over a distance of 0.150 m. How much work does the player do on the puck? What is the change in puck’s energy? Does the sign make sense?
Example Problem #2 • Juan lifts a potted plant into the air. If he gives the plant 90 J of potential energy in 0.65 seconds, how much power did Juan develop?
Example Problem #2 • Juan lifts a potted plant into the air. If he gives the plant 90 J of potential energy in 0.65 seconds, how much power did Juan develop?
Example Problem #3 • A skater with a mass of 52 kg moving at 2.5 m/s glides to a stop over a distance of 24.0 m. How much work did the friction of the ice do to bring the skater to a stop?
Example Problem #3 • A skater with a mass of 52 kg moving at 2.5 m/s glides to a stop over a distance of 24.0 m. How much work did the friction of the ice do to bring the skater to a stop?
Rest of Class • Power Practice Worksheet • Work quietly with 1 other person SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
Homework: Due Thursday • Finish Power Practice • Physics Update #3 • Based off notes from today. SWBAT solve simple power problems. SWBAT solve work-energy theorem problems.
