04_30_FR_Power - can the power plant light Think ∆ PE of...

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Today4/30 o Questions? o Power (Joules/second)
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Power o Energy moves from PE to KE, is lost to friction, is lost to heat and light, --In general can move from form to form. o The rate energy moves is called “Power” o Units of J/s called Watts (W)
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Power example A 12V battery is connected to a 24 resistor. How much power is supplied by the battery? Energy conservation says the same power will be dissipated by the resistor as heat. Think V means J/C and current means C/s P = IV V = IR I = 12/24 = 0.5A P = (0.5)12 = 6W
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Power example A hydroelectric plant makes power where water drops 50m through the turbines. If 10 6 kg of water per second move through the turbines, how many 100W light bulbs
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Unformatted text preview: can the power plant light? Think ∆ PE of the water per second P = ∆ PE/s and Energy conservation says this must be the same as the power output of the plant. ∆ PE/kg = mgh = 1(10)50 = 500J/kg P = ∆ PE/s = ( ∆ PE/kg)(#kg/s) = 500 x 10 6 W or 5 million 100W light bulbs Power example A rope pulls a brick across a rough table at a constant speed of 3m/s. The friction force is 40N. What power is supplied by the person pulling the rope? Think Work = Force x Distance P = Work/s and Energy conservation says this must be the same as the power output of the person. Work/m = 40(1) P = Work/s = (Work/m)(#m/s) = (40)(3) = 120W...
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