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Understanding Work and Power: Definitions, Calculations, and Applications

This lesson explores the scientific definition of work, contrasting it with everyday notions of labor. It explains that for work to occur, force must cause displacement, using examples that illustrate when a task does not qualify as work. The lesson includes practical calculations, guiding learners through formulas for work and power. With exercises involving pushing objects, lifting weights, and the functions of everyday appliances, students will apply their understanding of physical principles to determine work done and power exerted in various scenarios.

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Understanding Work and Power: Definitions, Calculations, and Applications

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  1. Name __________________________ Date ___________ Line ________ Work The science definition of work is very different from our normal definition of work. Two things must be true in order for work to be done A person is pushing on a wall. He is sweating hard and considers it hard work, but why is this NOT WORK?? ___________________________________ ___________________________________ A person carrying a stack of books while walking. She is huffing and puffing and considers it hard work, but why is this NOT WORK?? ___________________________________ ___________________________________

  2. Let’s calculate work! Your work formula: You push a refrigerator with a force of 100N. If you move the refrigerator a distance of 5m how much work is done? Let’s calculate power! You lift a crying baby from a crib with 50 J of work. It takes you 5 seconds. How much power is needed? COMBINE BOTH FORMULAS: A person pushes a couch with 100 N of force. It moves 5 meters and it takes him 2 seconds to do this. What was his power?

  3. Name __________________________________________ Date __________ A lawn mower is pushed with a force 1000 N. If 5000 J of work is done in mowing a lawn, what is the distance the lawn mower was pushed? The brakes on a bike do 2000 J of work in stopping the car. If the car travels a distance of 100 m while the brakes are being applied, what is he force the brakes exert on the bike? You push a box with a force of 20 N. It doesn’t move. What is the work done? A light bulb converts electrical energy into light and heat at a rate of 75 J every second. How many watts is the light bulb?

  4. If a runner’s power is 80 W, what is the work done by the runner in 5 seconds? How long will it take a car motor to do 5000 J of work if it uses 50 W of power? You lift a stack of books and do 200 J of work in 5 seconds. What is the power? You toss a baseball in the air and use 50 W of power in 2 seconds. What is the work done?

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