Energy and Work
DESCRIBE THE CONSERVATION OF ENERGY AND HOW ENERGY RELATES TO WORK. Energy and Work
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
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
Problem Answer An 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 = kg g = -9.8 m/s2 d = -3 m PE = ? PE = mgh PE = (.125)(-9.8)(-3) PE = J KE = J Sample Problem
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