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Work PS-6.3 Explain work in terms of the relationship among the force applied to an object, the displacement of the object, and the energy transferred to the object. PS-6.4 Use the formula W = Fd to solve problems related to work done on an object. Work • The product of: – the force applied to an object and – the displacement the object is moved, in the direction of the force • Work, force, and displacement are quantities that have magnitude and direction What do you think? Work • In order to do work on an object… – A force must be applied to the object – The object must move in the direction of the force (displacement) Work and Energy • When work is done on an object, energy is transferred to that object. – Work is equal to the change in energy – When a net force is applied to an object and it moves, the work is transformed to kinetic energy • The kinetic energy will be greater if – A greater force is added – If it is applied over a greater distance Which takes more work? • Suppose the ramp and staircase was the same height. Would it take more work to lift a ball to the top or to roll it up the ramp to the top? Height • If an object is lifted to some height, it gains gravitational potential energy equal to the work done against gravity to lift it to that height – The work done against gravity is the same whether the object was lifted straight up or rolled up a ramp – The greater the height, the more gravitational potential energy the object has Work Formula • Work = Force * displacement • W = Fd – Work is measured in Joules (J) • F=W/d – Force is measured in Newton’s (N) • d=W/F – Displacement is measured in meters (m) W F d Example 1 • A fork lift moves 34m carrying a 1023N box across the warehouse floor. How much work is done by the fork lift? W = Fd W = 1023 N * 34 m W = 34,782 J Example 2 • How much work is done by a person who uses a force of 27.5N to move a grocery buggy 12.3m? W = Fd W = 27.5 N * 12.3 m W = 338.25 J Example 3 • You and 3 friends apply a combined force of 489.5N to push a piano. The amount of work done is 1762.2J. What distance did the piano move? d=W/F d = 1762.2 J / 489.5 N d = 3.6 m Example 4 • 55, 000J of work is done to move a rock 25m. How much force was applied? F=W/d F = 55,000 J / 25 m F = 2,200 N Practice 1. Calculate the amount of work done when moving a 567N crate a distance of 20 meters. 2. A fallen tree is lifted 2.75 meters using a force of 1565N. How much work is done? 3. If it took a bulldozer 567.6 joules of work to push a mound of dirt 30.5 meters, how much force did the bulldozer have to apply? 4. A frontend loader needed to apply 137 Newton's of force to lift a rock. A total of 223 joules of work was done. How far was the rock lifted? 5. A young boy applied a force of 2,550 Newton's on his St. Bernard dog who is sitting on the boy's tennis shoes. He was unable to move the dog. How much work did he do trying to push the dog? 6. If it takes 68 joules of work to push a desk chair across a floor 12m, what force would be needed? 7. If a long distance runner with a weight of 596.82 newtons does 35,674.7 joules of work during a portion of a race, what distance will she cover during that portion?
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