Energy
Students will:
a) Identify several forms of
energy.
b) Calculate kinetic energy for
an object
c) Calculate potential energy
for an object
1
Kinetic Energy
• Kinetic Energy is the
energy of an object due
to its motion.
2
Kinetic Energy
KE mv 1
2
2
m mass
v velocity
3
Kinetic Energy
•Sample Problem 5B.1
A 7.00 kg bowling ball
moves at 3.00 m/s.
How much kinetic energy
does the bowling ball
have?
4
Kinetic Energy
• Sample Problem 5B
mb = 7.00 kg KEb = ?
vb = 3.00 m/s
KEb = (½)mv 2
KEb = (½)(7.00 kg)(3.00 m/s)2
KEb = 31.5 J 5
Kinetic Energy
•Sample Problem 5B.2
How fast must a 2.45 g
ping-pong ball move in
order to have the same
kinetic energy as the
bowling ball?
6
Kinetic Energy
•Sample Problem 5B.2
mpp = 2.45x10-3 kg KEb = 31.5 J = KEpp
KEpp = (½)mtvt2 vpp = ?
31.5 J = (½)(2.45x10-3 kg)vpp2
( 2)( 31.5J )
v pp
( 2.45 10 3 kg )
vpp = 1.60x102 m/s (358 miles per hour)
7
Kinetic Energy
Problems
p 174 #1-5
Work on this
assignment for
30 minutes. 8
P 174 #1-5
9
Kinetic Energy
Problems p 174
1) v = 170 m/s
2) v = 38.8 m/s
3) KEA = 2.4 J KEB = 4.8 J
4) KEA = 2.4 J KEB = 9.6 J
5) m = 1600 kg
10
Potential Energy
• Potential Energy is the
energy of an object due to
the position of the object.
11
Gravitational
Potential Energy
• Gravitational potential
energy is associated with an
object due to the position of
the object relative to the
Earth or some other
gravitational source.
12
Gravitational
Potential Energy
PE g = mgh
m = mass
g = gravity
h = height
13
Elastic
Potential Energy
• Elastic potential energy is
the potential energy in a
stretched or compressed
spring.
14
Elastic
Potential Energy
PEelastic = kx 1
2
2
k = spring constant
x = distance compressed
or stretched
15
Potential Energy
•Sample Problem 5D
A 70.0 kg stuntman is attached to a
bungee cord with an unstretched length of
15.0 m. He jumps off a bridge spanning a
river from a height of 50.0 m. When he
finally stops, the cord has a stretched
length of 44.0 m. Treat the stuntman as a
point mass, and disregard the weight of
the bungee cord. Assuming the spring
constant of the bungee cord is 71.8 N/m,
what is the total potential energy relative
to the water when the man stops falling?16
Potential Energy
•Sample Problem 5D
m = 70.0 kg k = 71.8 N/m
h = 50.0 m – 44.0 m = 6.0 m
x = 44.0 m – 15.0 m = 29.0 m
Peg = ?
PEelastic = ?
PEtotal = ?
17
Potential Energy
PE g mgh
PE g 70.0 kg 9.81 s 2 6.0 m
m
PE g 4100 J
PE elastic 1 kx 2
2
PE elastic 1
2
71.8 m 29 m 2
N
PE elastic 30200 J
PE total PE g PE elastic
PE total 4100 J 30200 J
PE total 34300 J 18
Potential Energy
Problems
p 180 #1-3
Work on this
assignment for
30 minutes.
19
P 180 #1-5
20
Potential Energy
Problems p 180
1) PEelastic = 3.3 J
2) PEelastic = 0.031 J
3) a) PEg = 785 J
b) PEg = 105 J
c) PEg = 0.00 J 21