Chapter 15
Energy Assignments
15.1 Math Skills 1-3 p 448; AQs 1-9 p452
15.2 Math Skills 1-3 p 458; AQs 1-6 & 9-10
15.1 Learning Targets for Energy
and its Forms
Describe the relationship between work and
energy
Calculate the kinetic energy of an object
given the objects mass and velocity
Analyze how potential energy is related to
an object’s position and give examples of
gravitational and elastic potential energy
Solve equations that relate an object’s
gravitational potential energy to its mass
and height
Give examples of the major forms of energy
MP 1.
A 70.0-kilogram man is walking at a speed of
2.0 m/s. What is his kinetic energy?
KE
KE
KE
KE
=
=
=
=
½ m*v2
0.5 * 70.0 kg * (2.0 m/s)2
0.5 * 70.0 kg * 4.0 m/s
140 J
MP 2.
A 1400-kilogram car is moving at a speed of
25 m/s. How much kinetic energy does the car
have?
KE
KE
KE
KE
=
=
=
=
½ m*v2
0.5 * 1400 kg * (25 m/s)2
0.5 * 1400 kg * 625 m/s
437,500 J
MP 3.
A 50.0-kilogram cheetah has a kinetic energy of
18,000 J. How fast is the cheetah running?
(Hint: Rearrange the equation to solve for v.)
KE = ½ m*v2
18,000 J = 0.5*50.0 kg*v2
18,000 J = 25*v2 (divide both sides by 25)
720 J = v2 (take the square root of both sides)
v = 26.8 m/s
1. Describe the relationship
between work and energy.
Energy is the ability to do work, and
work is the transfer of energy
2. How is the kinetic energy of an
object determined?
KE = ½ m*v2
3. What factors determine the
gravitational potential energy of an
object?
Its mass
The acceleration due to gravity
Its height
PE = m*g*h
4. Give an example of each of the
major forms of energy.
Chemical – wood, gasoline
Electrical – ipod
Mechanical – bouncing ball
Electromagnetic – light
Nuclear – nuclear power plants
Thermal – molten steel, fire
5. When you heat a pot of water over a
flame, what form of energy is added to
the water?
Thermal
6. Applying Concepts What kind of
energy is represented by an archer
stretching a bow string?
Elastic potential energy
7. Applying Concepts Can an object have both
kinetic energy and potential energy at the same
time? Explain
Yes, KE & PE are not mutually
exclusive
E.g. a falling leaf
8. A 60.0-kg person walks from the ground to
the roof of a 74.8-m-tall building. How much
gravitational potential energy does she have at
the top of the building?
PE = m*g*h
PE = 60.0 kg*9.8m/s/s*74.8m
PE = 44,000 J
9. A pitcher throws a 0.145 kg-baseball at
a velocity of 30.0 m/s. How much kinetic
energy does the ball have?
KE
KE
KE
KE
=
=
=
=
½ m*v2
0.5*0.145 kg*(30.0 m/s)2
0.5*0.145 kg*900 m/s
65.3 J