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Energy
Work – A force that acts through a distance. What is needed to perform work?
Conservation of Energy states that….
Different forms of Energy:
Objects can have different kinds of energy. In this unit, we will concentrate on the Mechanical Energy
of the objects.
Kinds of Mechanical Energy:
Potential Energy (PE)
Gravitational Potential Energy (PEg)
Spring Potential Energy (PEs)
Kinetic Energy (KE)
Total Mechanical Energy (ET)
An object can have PEg, PEs, and KE as part of it's total Mechanical Energy. When does an object
have mechanical energy?
 Objects have energy when they have HEIGHT,

if they are MOVING, or

if they could SPRING BACK TO SHAPE
(like a spring, rubber band or diving board).
Potential Energy:
A 257 kg pumpkin is suspended from a crane, 65 m above the ground. How much energy does the
pumpkin have before it is dropped?
A performer is tossed in the air at a parade. How much gravitational potential energy does the 60 kg
performer have when she is at a height of 5.2 m?
Kinetic Energy:
How much kinetic energy does a 105 kg snow ball have as it is rolled at a constant velocity of 2 m/s?
How much energy does a 1350 kg car have as it is driven at a constant velocity of 15 m/s?
What is the car's energy when the speed is doubled?
Total Energy
An object can have more than one kind of energy. The total mechanical energy of an object = stored
energy of the object + energy of motion
A 48 kg child (including sled) is sledding down an icy slope. How much energy does the child have
when he is going 5 m/s and is 15 m from the bottom of the hill? (ignore friction)
Conservation of Energy
Energy is neither created nor destroyed. Energy can only
be transformed from one form to another.
The total energy of the object remains constant if no external work is performed on the object.
(no external work such as a push or pull or friction) Since no work is done on the object, there is no
change in the total energy of the object, so.....
Examples: frictionless pendulums, frictionless roller coasters, frictionless slopes, free falling objects
and projectiles (neglect air resistance)
What happens to the potential energy as an object falls to the ground? What happens to the kinetic
energy as it falls to the ground? What happens to the total energy of the object?
Problems:
1. Amanda throws a 2 kg ball at an upward velocity of 9 m/s. How high will the ball go?
(4.13 m)
2. A 7kg bowling ball is held 5 m from the ground and released.
 What is the total energy of the bowling ball at the initial position?
 What is the bowling ball's PE at the initial position?
 What is the bowling ball's total energy just before it hits the ground?
 How fast is it going just before it hits the ground?
3. Devyn is riding on a frictionless roller coaster. She and the cart have a mass of 200 kg. She begins
from rest on top of a 20 m hill. How much energy does she and the cart have? (ETA)
How fast is she going at positions B, C and D?