1. Work and Energy Work Done W = Fd Units and Direction
Positive and Negative Work
When Work = 0

2. Work
Work (W) is the energy transferred to an object when a force acting on the object moves it through a distance
W = F x d
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4. Work Done Work is done when you lift an object _______
Work is done to make a car accelerate

5. Work
Consider a situation where you are pulling a bag on wheels at an angle Θ to the displacement
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7. Units and Direction Work is scalar and has no direction
Its units are Nm = J
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Stop at 3:42

8. Positive or Negative Work
If the force and displacement are in the same direction, work is “+”. If F and d are in opposite directions, work is “-”
Work is positive, negative, or zero, depending on the angle between the force and the displacement.
d = r
Try an example on your own for each

9. If velocity is constant, isn’t a = 0 and therefore, F = 0 and W = 0?
Whenever you talk about the work done, you must be very careful to specify which force does the work.
i.e. if the object is moving at a constant v
Wfriction= Ff x d
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Wapp = Fapp x d
Wnet = Fnet x d
x = +1 m
Ffriction
Fext = 10 N

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11. Check Your Understanding
N of force is applied to a cable used to tow a car as seen below 20.0 km. How much work is being done? Your answer should be in megajoules (1,000,000 J = 1 MJ).

12. Check Your Understanding
A store clerk moved a 4.4-kg box of soap without acceleration along a shelf by pushing it with a horizontal force of magnitude 8.1 N. If the employee did 5.9 J of work on the box, how far did the box move?

13. Check Your Understanding
A toboggan carrying two children (total mass = 85 kg) reaches its maximum speed at the bottom of a hill, and then glides to a stop in 21 m along a horizontal surface. The coefficient of kinetic friction between the toboggan and the snowy surface is 0.11.
Draw an FBD of the toboggan when it is moving on the horizontal surface.
Determine the magnitude of kinetic friction acting on the toboggan.

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15. Check Your Understanding
A bag of groceries of mass 8.1 kg is raised vertically without acceleration from the floor to a countertop, over a distance of 92 cm. Determine
the force needed to raise the bag without acceleration
the work done on the bag of groceries against the force of gravity

16. Check Your Understanding
A student pushes against a large maple tree with a force of magnitude 250 N. How much work does the student do on the tree?

17. Check Your Understanding
A 500-kg meteoroid is travelling through space far from any measurable force of gravity (F approaches 0). If it travels at 10,000 km/h for 100 years, how much work is done on the meteoroid?

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19. Zero Work Done - Summary
When W = 0
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