The document discusses work and energy, defining work as being done when a force causes an object to be displaced. It provides the work formula of work equals force times distance and explains that work is only done when the force and displacement are parallel. Several examples are given to illustrate when work is and isn't done based on whether the force and displacement are parallel.

1. Chapter 5: Work and Energy

2. • 1st characteristic: Work is done when the force
applied causes a displacement of the object
(the object moves)

3. Work formula

4. In which figure, the man is doing a
work? Fig A since he’s applying a force
to make the ball in motion

5. Is work done on the bag? No because
force is applied but the object is not
moving so displacement = 0
so W = F x 0 = 0 J

6. Sample Problem
Your car has run out of gas. Fortunately, there is a gas
station nearby. You must exert a force of 715 N on the
car in order to move it for 38 meters. Calculate the work
done to move the car.
Given : F= 715 N , d= 38 m
Unknown: W=??
Formula : W = F x d = 715 x 38 = 27170 J

8. 2nd characteristic: Work is done when the force
applied and the motion of the object are parallel
to each other

9. Hint: research for the following to justify your answer
1.Definition/Characteristics of work
2. Work Formula Analysis
3. Examples of situations where work is done and justification
using the formula

11. If F and d are not parallel

12. Work Formula

13. Formulas to get W or F or d

14. Problem 2
A girl playing tug-of-war with her dog pulls the dog a distance of 8.0 m
by exerting a force at an angle of 18° with the horizontal. If the amount
of work the girl does in pulling the dog is 190 J, what is the magnitude
of the force?
Given: d = 8m angle = 18 °
Unknown: F =???
Formula : W = F x d x cos O so
W = 190 J
Answer: F = 190 / (8 x cos 18) = 25 N

15. Is work negative or positive?
• an applied force can either cause a moving
object to speed up  work is positive
• an applied force can either cause a moving
object to slow down  work is negative

16. Work done is positive

17. Work done by air resistance is negative

18. Problem 3: Use the formula
w = F x d x cos O to explain in which figure work
is done

19. • Fig A : Force and Motion are parallel so the angle between them
= zero
so W = F x d x cos o= F x d x 1 = F x d. Work is done
• Fi B : Force and Motion are perpendicular so the angle between
them = 90 degrees
W = F x d x cos 90 degree = F x d x 0 = 0 J No work is done.
• Fig C : Force and Motion are parallel so the angle between them
= zero
so W = F x d x cos o= F x d x 1 = F x d. Work is done

20. Problem 4: If a neighbor pushes a lawnmower
four times as far as you do but exerts only half
the force, which one of you does more work and
by how much? Show your work.
W (neighbor)= 4 d x F/2 = 2 x d x F
So the neighbor does twice the work that I do

21. Problem 5: If a neighbor pushes a lawnmower
half the distance you’re pushing and exerts half
the force you do, which one of you does more
work and by how much? Show your work.
W (neighbor) = F/2 x d/2 =
So the neighbor does 1/4 the work that I do (or
you can say I do four times his work)

22. Bonus Problem 6:
The largest turtle ever caught in the United States had a mass of
800 kg. Suppose this turtle was raised 5.45 m onto the deck of a
research ship. What is the work it takes to lift the turtle this
distance at a constant velocity?