1. Energy and Work

2. DESCRIBE THE CONSERVATION OF ENERGY AND HOW ENERGY RELATES TO WORK. Energy and Work

3. Terms and Definitions Potential Energy Potential Energy  The energy that an object has because of position Kinetic Energy Kinetic Energy  The energy of an object due to the object’s motion Work Work  Transfer of energy to an object by the application of a force that causes the object to move in the direction of the force Power Power  A quantity that measures the rate at which work is done

4. Equations VariableEquationMKS Units English Units Potential Energy PEPE = mghJoules (J)ft x lbs Kinetic Energy KEKE=½mv 2 Jft x lbs WorkWW = FdJft x lbs PowerPP = W/tWatts (W)ft x lbs/s

5. Problem Answer An 0.125 kg apple is hanging on a tree 3 meters high. How much potential energy does the apple have? The apple falls. How much kinetic energy will it have when it hits the ground? m = 0.125 kg g = -9.8 m/s2 d = -3 m PE = ? PE = mgh PE = (.125)(-9.8)(-3) PE = 3.675 J KE = 3.675 J Sample Problem

6. Problem Answer A crane uses an average force of 5,200 N to lift a girder 25 m. How much work does the crane do on the girder? How much power was needed if it took 50 seconds to lift the girder? F = 5,200 N d = 25 m W = ? W = Fd W = (5,200)(25) W = 130,000 J t = 50 s P = W/t P = 130,000/50 P = 2600 W Sample Problem