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Work Energy Kinetic Energy Potential Energy Mechanical Energy Conservation of Mechanical Energy

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## Work Energy Kinetic Energy Potential Energy Mechanical Energy Conservation of Mechanical Energy

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**Work**• Energy • Kinetic Energy • Potential Energy • Mechanical Energy • Conservation of Mechanical Energy**ENERGY**• The capacity to do work • The energy transferred to an object equals the work done on the object ET = W**Energy is present in many forms**• Heat (thermal energy) • Kinetic Energy = “Motion Energy” • Potential Energy = “Stored Energy” • Mechanical energy – Sum of Potential and Kinetic • Nuclear • Sound • Electromagnetic energy • Chemical energy**The parallel component does work**The (F cos ) component does work**NO work done if there:**• Is no movement • The force if perpendicular to the displacement**In which photo(s) is WORKbeing done?**no yes yes no**If a 10 Newton force displaces a 20 kg block 40 meters**calculate the work done on the block by the force. F = 10N EXAMPLE The Normal force (FN ) and weight (mg) do no work in this problem, WHY?**Work = Force Distance**• The component of force parallel to the displacement DOES WORK • The perpendicular component DOES NO WORK • - Between the force and displacement • Scalar • Measured in Joules (J)**Positive Work - Force and displacement in same direction.**Negative Work - Force opposite the displacement. Zero Work - Force is perpendicular to the displacement. F d F d F d**If the Force is in the Direction of Motion:**In this case, = 0 o, so: If the Force is in the Opposite Direction of Motion: In this case, = 180o, so:**If the Force is Perpendicular to the Direction of Motion:**In this case, = 90 o, so: If the Object Being Pushed Doesn't Move: In this case, x = 0, so:**F= 10 N**300 A 10 N force acts 300 above the horizontal and displaces an object 5 meters horizontally how much work is done? W= F d cos = (10N)(5m) cos 300 = 43.3 J**How much work does gravity do on a 70 kg**person who falls 100 meters in the free fall ride?**Kinetic energy (KE) is the energy of a moving object.**• Energy associated with motion and mass.**A 500 kg car is traveling at 10 m/s, 10 sec. later it is**traveling 30 m/s. Calculate the following: • The initial kinetic energy • The final kinetic energy • The change in KE**Work Energy Theorem: The change in kinetic energy equals the**work done.**The animation shows a block of mass and initial speed v**sliding across a floor that is not frictionless. A kinetic friction force fk stops block during displacement d. Thus we can relate work done by friction to the change E in the system's energy**For hammer:**Moving hammer can do work on nail! For nail:**Matt’s little red wagon with a mass of 4.6 kg moves in a**straight line • on a frictionless horizontal surface. It has an initial speed of 10 m/s • and is pulled by Matt 4.0 m with a force of 18N in the direction of • the initial velocity. Use the work-energy relation • (WNet = KE) to calculate the wagons: • Change in Kinetic Energy • Final speed.**In a test of old sports car, it’s found that engines**provided around 1,000 N of force. If the typical mass is 400 kg and they accelerate from rest, how fast will they be going 100 m down the road?**How much work is done holding a box in place on an incline?**How much work is done pushing a 15 kg box up a 30° incline at a constant speed for 3 m**Force vs. Distance**Area under curve equals the work done**Force vs. Distance**Area under curve equals the work done**Area above the curve – work is positive**Area below the curve – work is negative**Work done by a variable force**equals Area under the curve**Gravitational Potential Energy (PE): The energy an object**has due to its height above a reference point. The potential energy change is independent of the path between the initial and final points. link**PE=mgh**Can gains Potential Energy equal to mgh**One serving of Bagel Crisps contains 543 kJ. How many**pull-ups are needed to burn it off? • M = 60 kg ∆h = .5 m • ∆PE = mg ∆H • 543000J = (60kg)(9.81N/kg)(.5m)(n) • 1845 = n • But the human body is only abour 20% efficient so, n is only 369!**Who does more work in lifting the respective equal masses to**the top of the incline at a constant speed?**1. His initial potential energy with respect to the ground**2. His potential energy 1 seconds after being released 3. His change in potential energy 4. Where did its energy go when it hits the ground? Rufus the 5 kg cat falls 10 meters from above the surface of the earth. Calculate:**Conservative Force: The work done is independent of the**path taken. Only depends on the initial and final position. Ex: Gravity Non Conservative Force: The work done depends on the path taken. Ex: Friction