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Chapter 5
Energy
1.
Dot product of vectors
2.
Kinetic Energy
3.
Potential Energy
4.
Work-Energy Theorem
5.
Conservative and non-conservative forces
6.
Conservation of Mechanical energy
7.
Non-conservative forces and conservation of
energy
8.
Power
9.
Work done by a variable force
Forms of Energy
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What is energy?
How many types of energy?
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Mechanical
Chemical
Electromagnetic
Nuclear
Transformation of energy
Multiplication of two vectors
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What is a dot
product?
What does it
give?
How do I
calculate it?
Work
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What is work?
How do I represent
it?
What does it do?
How do I calculate it?
What about units?
Is it a scalar or a
vector
What about friction?
Example - Work
1.
A force of F=50 N
is applied to a block
at an angle of θ=30
degrees to the
horizontal, the
block moves on the
horizontal surface
(which is
frictionless) by
∆x=3m, find Work
done on the block.
Work
Kinetic Energy (KE)
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What is Kinetic Energy?
How do I calculate it?
What are its SI units?
Is work related to Kinetic Energy?
Example - Kinetic Energy
1.
A 2.0 g bullet leaves the barrel of
a gun at a speed of 25 m/s. Find
a)
b)
The kinetic energy of the bullet.
The average force exerted by the
expanding gasses on the bullet as
the bullet moves the length of the
42 cm long barrel.
Gravitational Potential
Energy (PEg)
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What is
Gravitational
Potential Energy?
How do I calculate
it?
What are its SI
units?
Reference levels
Example - Work and
Potential Energy
1.
If a woman lifts a 21.0 kg bucket
from a well and does 4.0 kJ of
work, how deep is the well?
Assume that the speed of the
bucket remains constant as it is
lifted?
Work-Kinetic Energy
Theorem
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What is this
theorem?
What if the work
is positive or
negative?
Work-Energy Theorem
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Mechanical Energy
What is this theorem?
Work-Energy Theorem
1.
A 800 N skier
and sled is at the
top of a slope,
as shown. At
point A she has
a velocity of
5m/s. Find her
speed when she
is at point B.
Nature of Forces
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What are conservative
forces?
Examples of
conservative forces?
What are nonconservative forces?
Examples of nonconservative forces?
Internal Energy
Table is frictionless
Table is NOT frictionless
Work and Potential Energy
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What is the relationship between
work and potential energy?
When is this relationship true?
What is the relationship?
Conservation of
Mechanical Energy
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What is conservation of energy?
Can we prove it?
xo,yo
Vi=0
5m
Vf=?
Example – Conservation of
Energy
1.
A 0.4-kg bead
slides on a curved
wire, starting from
rest at point A as
shown. If the wire
is frictionless, find
the speed of the
bead at B and at
C.
Work-Energy Theorem for
non-conservative forces
Example – Conservation of
Energy
1.
A 0.4-kg bead slides on a
curved wire, starting from
rest at point A as shown.
If the wire is frictionless
between A and B and
rough between B and C,
find the speed of the
bead at B and if the wire
comes to rest at C, find
the loss in mechanical
energy as it goes from B
to C.
Potential Energy Stored in
a Spring
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What is a spring?
What does it do?
How do I calculate
the force due to a
spring?
What is a spring
constant?
How do I calculate
the work done by
a spring?
Work-Energy Theorem Including
a Spring- non conservative force
Conservation of Energy
Including a Spring
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Spring - Example
1.
A spring that has a force
constant of 1.0x103N/m is
placed on a table in a vertical
position as shown. A block of
mass 1.60 kg is held 1.0m
above the free end of the
spring. The block is dropped
from rest so that it falls
vertically onto the spring. By
what distance does the spring
compress?
Power
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What is power?
How do I calculate it?
What are the SI units?
Power, cont.
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US Customary units are generally hp
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Need a conversion factor
ft lb
1 hp  550
 746 W
s
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Can define units of work or energy in terms
of units of power:
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kilowatt hours (kWh) are often used in electric
bills
This is a unit of energy, not power
Example – Power
1.
A load is
lifted by a
motor at a
constant
speed of 3.0
m/s. Find the
power the
motor must
deliver
Example – Power
1.
Water flows over a section
of Niagara Falls at the rate
of 1.2x106 kg/s and falls
50 m. How much power is
generated by the falling
water?
Center of Mass & Vertical
Jumps
Work Done by Varying
Forces
Work done by Spring
Varying Force - Example
1.
The figure shows the force acting
on an object as a function of
distance. Calculate the total work
done?