1. Chapter 5
Work and Energy

2. Work and Energy
Work
Energy
Conservation of Energy
Power

3. Everyday vs. Scientific Work

4. 1 Joule (J) = 1 Newton × 1 meter
Definition of Work
Work =
component of force in the direction of displacement ×
magnitude of displacement
Units of Work
1 Joule (J) = 1 Newton × 1 meter

5. Definition of Work
𝑊=𝐹cos(𝜃)Δ𝑥 𝐹 𝜃 Δ𝑥

6. Which show positive work? Which show negative work?

7. If the object moves 5 m to the right, and the applied force is 2 N, how much work is done on the object?
60°
60°

8. Practice Two forces act on the 10-kg block below, causing it to accelerate from rest over the period of 3 seconds. What is the work done on the block if these are the only two forces acting on the block?
5 N
10 N

9. Quick Check Is work being done? Picking up a book off the floor
Carrying a lunch tray across the cafeteria
Pushing a parked car
Pulling a suitcase across the airport

10. ? ?
Energy
Mechanical ?
Kinetic
Potential

11. Connecting work to energy… Start with: 𝑊 net =𝐹Δ𝑥 and 𝑣 𝑓 2 = 𝑣 𝑖 2 +2𝑎Δ𝑥 𝑊 net = ?

12. the energy of an object due to its motion
Kinetic Energy
the energy of an object due to its motion
Units = ?
𝐾𝐸= 1 2 𝑚 𝑣 2

13. Practice Calculate the speed of an 8
Practice Calculate the speed of an 8.0×104 kg airliner with a kinetic energy of 1.1×109 J.

14. Work-Kinetic Energy Theorem
Work done by the object or work done on the object?
𝑊 net =Δ𝐾𝐸

15. Practice On a frozen pond, a person kicks a 10
Practice On a frozen pond, a person kicks a 10.0 kg sled, giving it an initial speed of 2.2 m/s. How far does the sled move if the coefficient of kinetic friction between the sled and the ice is 0.10? Ans=2.5 m

17. Potential Energy
the energy associated with an object due to its position, shape, or condition *Potential energy is relative

18. Energy
Mechanical
Kinetic
Potential
Gravitational
Elastic

19. Gravitational Potential Energy
ℎ is the height, relative to a zero level Units = ?
𝑃 𝐸 𝑔 =𝑚𝑔ℎ

20. 500 kg A
60 m C
25 m B

22. Elastic Potential Energy
𝑘 is the spring constant 𝑥 is the compressed or stretched distance Units = ?
𝑃 𝐸 elastic = 1 2 𝑘 𝑥 2

23. Elastic Potential Energy

24. REVIEW

25. Where is the maximum KE? Where is the maximum PE? Mechanical energy = ?

26. Conservation What does it mean that something is conserved?
Can energy be created or destroyed?

27. Conservation of Mechanical Energy
True only if there is no friction
𝑀 𝐸 𝑖 =𝑀 𝐸 𝑓

30. 500 kg A
60 m C
25 m B

32. the rate at which work is done Units = ? Another form of the equation?
Power
the rate at which work is done Units = ? Another form of the equation?
𝑃= 𝑊 Δt

33. Practice Two horses pull a cart. Each exerts a force of 250
Practice Two horses pull a cart. Each exerts a force of N at a speed of 2.0 m/s for 10.0 min. Calculate the power delivered by the horses. How much work is done by the two horses?