1. Work and Energy
Chapter 5
Mrs. Schwartz

2. What is work?

3. Work
Work is done on an object when a FORCE causes a displacement on an object.
W = Fd

5. Work
Work is only done when components of a force are parallel to the objects displacement.

6. W = Fd(cos θ) Work with an angle
If there is a force in a direction that makes an angle, θ, with the direction of the displacement, then
W = Fd(cos θ)
θ is the angle between the directions of the force and the displacement.

7. Work
If θ = 0 (parallel) then Cos0 = 1
Work is done!
If θ = 90 (parallel) then Cos90 = 0
No Work done!
Work is only done when components of a force are parallel to the objects displacement.

8. Example
How much work is done on a vacuum cleaner pulled 3.0m by a force of 50.0N at an angle of 30.0o above the horizontal?

9. Work Force in direction of motion speed increases positive work.
Force opposes motionspeed decreases negative work
Force is 90º to motion no work done
Object is not in motion no work done

10. Kinetic Energy Kinetic Energy is the energy of an object in motion.
K.E. = ½ mv2
This formula is derived from a motion formula and the work formula. Kinetic energy depends on an object’s mass and velocity.

11. Work-Kinetic Energy Theorem
The net work done on an object is equal to the change in the kinetic energy of the object.
Wnet = ΔK.E. = ½ mvf2 - ½ mvi2 = Fnetd