11.2 Energy and Power Key Question: How powerful are you? *Students read Section 11.2 AFTER Investigation 11.2

Power  Work is a measure of how much Energy was used or produced due to an applied force over a distance.  Power is a way to measure how fast the Energy was used or produced.  Basically, how fast you get work done over time determines how powerful you are

Power  A unit of power is called a Watt.  Named after the inventor of the Steam Engine, James Watt. There was no formal way to talk about power back then, and since people used horses to do work – they quantized it with the amount of horses needed: Horsepower.

11.2 Power Power is equal to the amount of work done divided by the time it takes to do the work. P = E t Change in work or energy (J) Change in time (sec) Power (W)

Energy and Power: The faster you use the energy, the more power you generate

Calculate power Bicycling up a steep 4 meter hill causes a cyclist to burn 800 J of caloric energy. If it took the cyclist 2.3 seconds to go up the hill, how much power did the cyclist generate in this time? P = E t

Calculate power from work  A 70 kg person goes up stairs 5 m high in 30 sec. How much power does the person need to use?  First, find the work or energy necessary: Work = Fd or U g = mg(  y) Work = (force of weight)distance Work = (mg)d

11.2 Calculate power  Now that we have the working energy, find the power used: P = E t

Now find power with Kinetic Energy: A 1500 Kg Truck on a racetrack travels at 30 m/s. If it completes a drag race in seconds, how much power did the engine generate? Find Energy: 30 m/s means it has speed/velocity so we need to find the Kinetic Energy used: K = ½mv 2 Find Power: