1. Work and Energy
Chapter 5
Physics

2. Work
5-1

3. 5-1 Learning Targets
Recognize the difference between scientific work and ordinary work.
Identify where work is being done.
Calculate net work when many forces are applied.

4. Work
1-Transfer of energy by applying a force that causes the object to move in the direction of the force
2-Must have movement to be work

5. W= Fnetdcosθ Work = force x distance Work measured in Joules (J)
J= 1Nm or 1kg m2/s2
Force measured in N
Distance measured in meters

6. Work Problem
A crane uses an average force of 5200 N to lift a grinder 25 m. How much work does the crane do on the grinder?
W= Fd
W= (5200N) x ( 25m) = J

7. 3- if there is an angle between the force and the direction of the displacement work is:

8. How much work is done on a lawnmower pulled 3. 0 m by a force of 60
How much work is done on a lawnmower pulled 3.0 m by a force of 60.0 N at an angle of 35.0º above the horizontal?
W=Fd cosΘ
W= ( 60.0 N) ( 3.0 m) (cos 35.0º)
W= 150 J

9. 4- when the force on an object and the objects displacement are in different directions
component of the force that is in the direction of the objects displacement does the work

10. 5- Work is done only when components of a force are parallel to a displacement
no net work is done on any object if the net force is perpendicular to the displacement (cos 90°= 0)

11. 6- if many constant forces are acting on an object find the net work done by first finding the net force
Wnet= Fnet d (cos Θ)

12. 7-Work is positive when the component of force is in the same direction as the displacement
8- work is negative when the force is in the direction opposite the displacement

13. 9- if net work is positive the object speeds up
Net force does work on the object
10- if net work is negative the object slows
Work is done by the object on another object