Potential Energy
Stored energy or energy due to
position/location
There are 2 types of potential
energy…
• 1. gravitational potential depends on
height of object from the zero level
• 2. elastic potential depends on the stretch
or compression of a spring or elastic
material
PEg=mgh
• m is mass in kg
• g is gravitational acceleration
• h is height above zero level in meters
Example1:
• A 70.0kg stuntman attached to a bungee
cord jumps off a bridge that is 50m above
a river. If the cord stops 6m above the
surface of the water, calculate the
potential energy of the stuntman just
before he is pulled back by the bungee
cord.
PEe=1/2 kx2
• k is “spring constant” which will be a given
90% of the time
• x is the difference between stretched and
un-stretched length of the spring or string
Example 2:
• If the stuntman form example 1 used a
bungee cord with an un-stretched length of
15m and a spring constant of 71.8N/m,
what is the potential elastic of the bungee
cord?
Conservation of Energy
• Energy will change from potential to kinetic
and back without loss or gain during a
“story” or situation.
Example 3:
• A 150lb woman hangs out the window of a
burning building. If the window is 25m above
the surface of the firemen’s net, what is her
potential energy?
• As she falls, her PE transfers into KE. If all of
her PE is converted over, how long will it take
her to reach the waiting firemen?
Homework:
• Page 172 #1-3 Top and Bottom!!!!