Tuesday May 21
Overview Energy
1. Motion
2. Object
3. Potential
4. Mechanical Energy
5. Chemical
6. Elastic
7. Chemical
8. Gravitational
9. Elastic
10.Gravitational
The nature of energy
1. Energy of a spinning
bicycle wheel
2. Energy stored in food
3. Energy stored in a
boulder on a ….
4. Energy stored in a
stretched string
5. Energy that is stored
6. Less
7. More
8. Energy
9. Joule
10. Potential,kinetic
11. Potential
12. Chemical
Chapter Test Continued
18) A
19) D
20) B
21) C
22) A
23) B
24) D
25) C
Understanding Concepts
1. A.
PE=mgh=10(9.8)(1.5)=147
J
B. PE=mgh=(10)(9.8)(1)= 98
J
2. KE= ½ mv2= .5(10)(10)(10)=
500 J
3. KE=PE=147 J
There are two types of potential
energy problems.
A 4.5 kg dictionary sits on
a 4.0 m high shelf. Find
its potential energy.
A 12-N copper ball sits on a
church stepple 40 m above
the ground. Find its potential
energy.
• PE=WH
• PE= mgh
• PE= 4.5 (9.8) 4 • PE= 12(40)
• PE=480 J
• PE= 176.4 J
An automobile to be transported
by ship is raised 7.0 m above the
dock. If its gravitational potential
energy is 66000 J, find its mass.
• Given
• Solution
An automobile to be transported
by ship is raised 7.0 m above the
dock. If its gravitational potential
energy is 66000 J, find its mass.
• Given
H= 7.0 m
A= 9.8 m/s/s
PE= 66 000 J
M= ?
•
•
•
•
•
Solution
PE=mgh
M=PE/gh
M= 66 000/9.8(7)
M= 960 kg
The world record for pole vaulting
is 6.15 m. If the athlete’s
gravitational potential energy is
4,942 J, what is his mass?
• Given
• Solution
The world record for pole vaulting
is 6.15 m. If the athlete’s
gravitational potential energy is
4,942 J, what is his mass?
•
•
•
•
•
Given
H= 6.15 m
PE= 4942 J
G= 9.8 m/s/s
M=?
•
•
•
•
•
Solution
PE=mgh
M=PE/gh
M= 4942/9.8(6.15)
M= 82 kg
Find the kinetic energy of a .045 kg
hockey puck traveling at 45 m/s.
• KE= ½ mv2
• KE= ½ (.045)
(45)(45)
• KE= 45.56 J
A baseball is pitched with a speed
of 35 m/s. Calculate its kinetic
energy if it has a mass of 0.146 kg?
• Given
• Solution
A baseball is pitched with a speed
of 35 m/s. Calculate its kinetic
energy if it has a mass of 0.146 kg?
•
•
•
•
Given
M= 0.146 kg
V= 35 m/s
KE= ?
•
•
•
•
Solution
KE= ½ mv2
KE= (.5)(0.146)(35)(35)
KE= 89 J
A “ping-pong” ball has a mass of
.00245 Kg and can be given a
speed of 4.0 m/s. Find its kinetic
energy?
• Given
• Solution
A “ping-pong” ball has a mass of
.00245 Kg and can be given a
speed of 4.0 m/s. Find its kinetic
energy?
•
•
•
•
Given
M= 0.00245kg
V= 4 m/s
KE= ?
•
•
•
•
Solution
KE= ½ mv2
KE= (.5)(0.00245)(4)(4)
KE= 0.0196 J
Potential Energy Worksheet
• 1. PE=mgh or PE=WH
• 2. Joule (J)
3. PE=WH
PE=12(21)
PE=252 J
Potential Energy Worksheet
4. PE=WH
PE=79(20)
PE= 1580 J
5.PE=WH
PE=190(45)
PE=8550 J
Potential Energy Worksheet
6.PE=WH
PE= 966(72)
PE= 69, 552 J
7.PE=mgh
PE=5(9.8)12)
PE= 588 J
Kinetic and Potential Energy
Worksheet
1 KE= ½ mv2
• KE= ½ 2.1(30*30)
• KE= 945 J
3 KE= ½ mv2
• KE= ½ (1120) 40 * 40
• KE= 8,960,000 J
Kinetic and Potential Energy
Worksheet
7. D
8. A
9. D
10.Friction.
Energy problems Worksheet
• 1. KE= ½ mv2
• KE= = .5(3) (5)(5)
• KE= 37.5 J
Energy problems Worksheet
• 2. PE=mgh
• PE= 6.5(9.8)(5)
• PE=166 J
Energy problems Worksheet
•
•
•
•
KE= ½ mv2
M= 2 KE/v2
M= 2(173)/(3.8 * 3.8)
M= 24 J
Energy problems Worksheet
•
•
•
•
PE=mgh
H=PE/mg
H=328/(7.5)(9.8)
H=4.5m
Energy problems Worksheet
•
•
•
•
•
•
•
•
5.
KE= ½ mv2
KE= ½ 30 (2*2)
KE= 60 J
KE= ½ mv2
KE= ½ 60 (2*2)
KE= 120 J
It doubles.
Energy problems Worksheet
•
•
•
•
•
•
•
•
•
6.
KE= ½ mv2
KE= ½ 30 (2*2)
KE= 60 J
KE= ½ mv2
KE= ½ 30 (4*4)
KE= 240 J
It is quadrupled.
Energy problems Worksheet
• 7.PE= mgh
PE= 4(9.8)(2)
PE=78.4 J J
PE=mgh
PE= 4(9.8)(4)
PE= 156.8 J
It doubled.
Energy problems Worksheet
• 8.
• KE= ½ mv2 . 4.2 m/s
• KE= ½ 12 (3*3)
Energy problems Worksheet
•
•
•
•
9.
KE= ½ mv2
2KE= m (52*52)
m= 72 kg
Energy problems Worksheet
10. PE= mgh
PE= 0.49(9.8)(3.6)
PE=17.3 J
PE=mgh
PE= 0.49(9.8)(1.5)
PE= 7.2 J
Decreased by 10.1 J