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Power Contents: Definition of Power Whiteboards Jambalaya Whiteboards. Power - The rate at which work is done. Power = Work/Time P = W/ t P = Power W - Work done t - Time to do work. A person does 145 J of work in 20.0 s. What is power output?

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## Power Contents: Definition of Power Whiteboards Jambalaya Whiteboards

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**Power**• Contents: • Definition of Power • Whiteboards • Jambalaya • Whiteboards**Power - The rate at which work is done**• Power = Work/Time • P = W/t • P = Power • W - Work done • t - Time to do work • A person does 145 J of work in 20.0 s. What is power output? • P = W/t = (145 J)/(20.0 s) = 7.25 J/s • = 7.25 Watts = 7.25 W • 1 horsepower = 745.7 Watts, 1 kW = 1000 Watts TOC**Power - The rate at which work is done**• power = work/time = (Fd)/t = F(d/t) = Fv • F = Force to move something • v = Velocity it is moving P = Fv My 30. HP van could go 25 m/s top speed. What was the force resisting its motion? 1 horsepower = 745.7 Watts, 1 kW = 1000 Watts power = (30 HP)(745.7 Watt/HP) = 22,371 W P = Fv 22,371 W = F(25 m/s), F = 890 N TOC**Whiteboards:**Power 1 | 2 | 3 | 4 | 5 TOC**Joe Mama does 613 J of work in 2.13 seconds. What is his**power output? P = W/t = (613 J)/(2.13 s) = 288 W W 288 W**Ima Wonder can put out 127 W of power. What time will it**take her to do 671 J of work? P = W/t, t = W/P = (671 J)/(127 W) = 5.28 s W 5.28 s**What work does a 1.5 HP motor do in 1 minute?**P = (1.5 HP)(745.7 W/HP) t = 60 s P = W/t, W = Pt = (1118.55 W)(60 s) = 67113 J W 67,000 J**Bob N. Frappels slides a box with 43 N of force at a**constant speed of 5.3 m/s. What is his power output? P = Fv = (43 N)(5.3 m/s) = 227.9 W = 230 W W 230 W**Frieda People can put out 430 W of power. With what speed**can she push a car if it takes 152 N to make it move at a constant velocity? P = Fv v = P/F = (430 W)/(152 N) = 2.83 m/s W 2.83 m/s**Power all mixed up**Things we can know P - Power (in W) W - Work (in J) F - Force (in N) d - distance (in m) t - time (in s) - coefficient of friction m - mass (in kg) v - Velocity (in m/s) a - acceleration (in m/s/s) Formulas: F = mg (Lifting) F = mg (Dragging) F = ma (Accelerating) P = W/t (Power) P = Fv (Power) W = Fd (Work) v = d/t (Velocity) a = v/t (Acceleration) Jambalaya! It’s a**P - Power (in W)**W - Work (in J) F - Force (in N) d - distance (in m) t - time (in s) - coefficient of friction m - mass (in kg) Formulas: F = mg (Lifting) F = mg (Dragging) P = W/t (Power) W = Fd (Work) Sample 1 - A 1.2 HP winch can lift a 2350 kg LandRover up 14.5 m into a tree in what time?**P - Power (in W)**W - Work (in J) F - Force (in N) d - distance (in m) t - time (in s) - coefficient of friction m - mass (in kg) Formulas: F = mg (Lifting) F = mg (Dragging) P = W/t (Power) W = Fd (Work) Sample 2 - Gumi Baere drags a 45.1 kg box that has a coefficient of friction between it and the floor of .34 a distance of 16 m in 11.7 seconds. What is her power output?**Whiteboards:**Power Jambalaya 1 | 2 | 3 | 4 TOC**What must be the power rating of a motor if it is to lift a**560 kg elevator up 3.2 m in 1.5 seconds? F = mg = (560 kg)(9.8 N/kg) = 5488 N W = Fd = (5488 N)(3.2 m) = 17561.6 J P = W/t = (17561.6 J)/(1.5 s) = 11707.7 W W 11700 W**A .75 HP winch can lift a car 5.2 m in 37 seconds. What**must be the mass of the car? 1 HP = 745.7 W P = (.75 HP)(745.7 W/HP) = 559.275 W P = W/t, W = Pt = (559.275 W)(37 s) = 20693.175 J W = Fd, F = W/d = (20693.175 J)/(5.2 m) = 3979.5 N F = mg, m = F/g = (3979.5 N)/(9.8 N/kg) = 406 kg W 406 kg**Red Elk leads a dog team that can put out 2.5 kW of power.**They skid a 312 kg sled a distance of 340 m in 93 seconds. What must be the coefficient of friction? P = 2500 W P = W/t, W = Pt = (2500 W)(93 s) = 232500 J W = Fd, F = W/d = (232500 J)/(340 m) = 683.8 N F = mg, = F/(mg) = (683.8 N)/((312 kg)(9.8 N/kg)) = .22 W .22**A 150 HP tractor can drag a 350 kg load how far in a minute**if the coefficient of friction between the load and the ground is .78. 1 HP = 745.7 W P = (150 HP)(745.7 W/HP) = 111855 W F = mg = (.78)(350 kg)(9.8 N/kg) = 2675.4 N P = W/t, W = Pt = (111855 W)(60 s) = 6711300 J W = Fd, d = W/F = (6711300 J)/(2675.4 N) = 2508 m W 2500 m

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