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P9_Energy_Power_Units

# P9_Energy_Power_Units - Energy and Power Recall Work...

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Energy and Power

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Recall: Work …crushed cans… To apply work I need: a force F and… … a displacement Δx In the same direction nt Displaceme Force Work = x F W =
Question A race car accelerates from 0m/s to 30m/s in 2.5s . Your own car does the same in 15s . Both weight 1000kg. Which car does more work ? A) Same B) The race car C) Your car Why does the race car need the bigger engine?

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4 Power Average Power The unit of power is the watt. 1 watt = 1 J/s = 1 W t E P = αω Power is the rate of energy transfer .
5 Power Fv P = Instantaneous Power (1-D) Fv t r F t W P t v r r F W = = = = =

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Units! Work (Energy) Unit: Joule Power Unit: Watt x F W = 2 2 1 1 Joule 1 s m kg m N = = v F t W P = = 3 2 1 s Joule 1 Watt 1 s m kg = =
7 Example : A race car with a mass of 500.0 kg completes a quarter-mile (402 m) race in a time of 4.2 s starting from rest. The car’s final speed is 125 m/s. What is the engine’s average power output?

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P9_Energy_Power_Units - Energy and Power Recall Work...

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