2. Work – in the physics sense of the word

3. Work – in the physics sense of the word

4. Work – in the physics sense of the word
Work is force times distance
(assuming the force is parallel to the displacement)

5. Work – in the physics sense of the word
Units: 1 N x 1 m = 1 N·m = 1 J (Joule)

6. Work – in the physics sense of the word
Units: 1 N x 1 m = 1 N·m = 1 J (Joule)

7. An intern pushes an 87 kg patient on an 18 kg gurney, producing an acceleration of 0.55 m/s2.
(a) How much work does the intern do in pushing the patient and gurney through a distance of 1.9 m? Ignore friction.

8. An intern pushes an 87 kg patient on an 18 kg gurney, producing an acceleration of 0.55 m/s2.
(a) How much work does the intern do in pushing the patient and gurney through a distance of 1.9 m? Ignore friction.
(b) How far must the intern push the gurney to do 140 J of work?

9. What if the force acts at an angle to the displacement?

10. What if the force acts at an angle to the displacement?

11. In a gravity escape system, an enclosed lifeboat on a large ship is deployed by letting it slide down a ramp and then continue in free fall to the water below. Suppose a 4970 kg lifeboat slides a distance of 5.00 m on a ramp, dropping through a vertical distance of 2.50 m. How much work does gravity do on the boat while it’s on the ramp?

13. Work can be negative

14. Three forces act on a car coasting down a hill.
Does each force do positive, negative, or zero work on the car?

16. The Work-Kinetic Energy Theorem
Derivation…

17. Kinetic energy is sometimes called the “energy of motion”
The Work-Kinetic Energy Theorem
Kinetic Energy:
Kinetic energy is sometimes called the “energy of motion”

18. Kinetic energy is sometimes called the “energy of motion”
The Work-Kinetic Energy Theorem
Kinetic Energy:
Kinetic energy is sometimes called the “energy of motion”
Units?

19. The Work-Kinetic Energy Theorem
Kinetic energy is sometimes called the “energy of motion”
Units?
NOTE: K is never negative.

20. A hockey puck with mass m sliding on ice with speed v has kinetic energy K.
What is its kinetic energy if we double its mass, keeping the speed at v?
A) K
B) 2K
C) 3K
D) 4K
E) 5K

21. A hockey puck with mass m sliding on ice with speed v has kinetic energy K.
What is its kinetic energy if we double its speed, keeping the mass at m?
A) K
B) 2K
C) 3K
D) 4K
E) 5K

22. The Work-Kinetic Energy Theorem
The net work done on an object is the change in its kinetic energy

23. When a father takes his son for a run in his stroller, he exerts a force of 35.0 N at an angle of 32.0º below the horizontal on the stroller. He exerts this force on the stroller over a distance of 2.75 m.
If the initial speed of the stroller was 0.65 m/s, what is the final velocity?