Energy and Work
Energy and Work
DESCRIBE
THE CONSERVATION OF ENERGY
AND HOW ENERGY RELATES TO
WORK.
Terms and Definitions
 Potential Energy

The energy that an object has because of position
 Kinetic Energy

The energy of an object due to the object’s motion
 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

A quantity that measures the rate at which work is done
Equations
Variable Equation
Potential
Energy
Kinetic
Energy
Work
Power
PE
PE = mgh
MKS
Units
Joules (J)
English
Units
ft x lbs
KE
KE=½mv2
J
ft x lbs
W
P
W = Fd
P = W/t
J
Watts (W)
ft x lbs
ft x lbs/s
Sample Problem
Problem
 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?
Answer
 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
Problem
Answer
 A crane uses an average
 F = 5,200 N
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?
 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