1. Chapter 15 Energy Assignments 15.1 Math Skills 1-3 p 448; AQs 1-9 p452

2. 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

3. MP 1. A 70. 0-kilogram man is walking at a speed of 2. 0 m/s
MP 1. A 70.0-kilogram man is walking at a speed of 2.0 m/s. What is his kinetic energy?
KE = ½ m*v2
KE = 0.5 * 70.0 kg * (2.0 m/s)2
KE = 0.5 * 70.0 kg * 4.0 m/s
KE = 140 J

4. MP 2. A 1400-kilogram car is moving at a speed of 25 m/s
MP 2. A 1400-kilogram car is moving at a speed of 25 m/s. How much kinetic energy does the car have?
KE = ½ m*v2
KE = 0.5 * 1400 kg * (25 m/s)2
KE = 0.5 * 1400 kg * 625 m/s
KE = 437,500 J

5. 18,000 J = 25*v2 (divide both sides by 25)
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

6. 1. Describe the relationship between work and energy.
Energy is the ability to do work, and work is the transfer of energy

7. 2. How is the kinetic energy of an object determined?
KE = ½ m*v2

8. 3. What factors determine the gravitational potential energy of an object?
Its mass
The acceleration due to gravity
Its height
PE = m*g*h

9. 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

10. 5. When you heat a pot of water over a flame, what form of energy is added to the water?
Thermal

11. 6. Applying Concepts  What kind of energy is represented by an archer stretching a bow string?
Elastic potential energy

12. Yes, KE & PE are not mutually exclusive E.g. a falling leaf
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

13. PE = m*g*h PE = 60.0 kg*9.8m/s/s*74.8m PE = 44,000 J
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

14. 9. A pitcher throws a 0. 145 kg-baseball at a velocity of 30. 0 m/s
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 = ½ m*v2
KE = 0.5*0.145 kg*(30.0 m/s)2
KE = 0.5*0.145 kg*900 m/s
KE = 65.3 J