1. Work, Energy and Power

2. Work in 1-D Work in 1-D with a constant force is Units - N·m or J (joules) Ex. While mowing the lawn, I press directly into the handle with a force of 80N. The handle makes an angle of 40° wrt. horizontal. How much work is done on the mower after it is pushed 25m?

3. Work of Friction On the previous problem, the lawn exerts a frictional force of 50N. How much work does it do on the lawnmower? F 

4. Work in 3-D Work in 3-D with a constant force is Only want component of force in the direction of the displacement. Work is a scalar. F rr  Scalar Product (Dot Product)

5. Dot Product With unit vectors Therefore,

6. Kite Flying During a strong gust of wind a kite rises vertically 2.5m and moves to the west 5.4 m. If the force from the gust of wind is 15N directed 20° upward from due east, what work was done on the kite by the gust of wind? F wind  rr

7. 1-D varying Force Work in 1-D with a varying force is Work on a Spring Assume x 0 = 0 Force you exert on the spring. F x Work you do on the spring Note: During the same motion the spring does negative work.

8. Compressed Spring How much work is done on a spring with a spring constant of 35 N/m if it is compressed 0.50m? F x

9. 3-D Varying Force Ex. How much work is done on a 5.0kg block by gravity as it slides down a parabola from x=1m to x=0m? For the parabola 0m -1m 1m Most general form of the definition of work This is called a line integral.

10. Kinetic Energy Kinetic Energy - Energy of Motion Work-Energy Theorem

11. Braking Car A 600 kg car is traveling at 24 m/s. The driver slams on the brakes and reduces the car’s speed to 13 m/s before hitting a stalled car. What work was done on the car while braking and what work was done on the car by the collision? v

12. Power Power - Rate at which energy is used or produced. –Average Power –Instantaneous Power –Units - watt (W) Ex. How much power does Alexeyev have if lifting the weight 2m in 3 s? At 157 kg and lifting 246 kg

13. Energy & Energy Transfer System/Environment –Kinetic energy –Internal energy –Potential energy Energy transfer –+Work (E → S) –Mechanical Waves –Heat –Matter transfer –Electrical transmission –EM radiation Environment System