Chapter 10 Energy, Work, & Simple Machines

1. Chapter 10 Energy, Work, & Simple Machines

2. 10.1 Energy & Work A force that causes a Displacement of an object does Work on that object.

3. Work is the product of the Magnitudes of the component Of a force along the direction And the displacement. W = Fd

4. Work has the dimensions of Force times length. Thus the units are N * m Or the Joule (J)

5. Work is only done when Components of a force are Parallel to a displacement. W = Fd (cos θ)

6. Problem... A tugboat pulls a ship with a force Of 5.00 X 103 N. How much work Is done by the tugboat on the Ship if it moves 3.00 km? 1.50 X 107 J

7. Problem... How much work is done on a Vacuum cleaner pulled 3.0 m by A force of 50 N at an angle of 30.0° above the horizontal? 130 J

8. Energy is The capacity to Do work or to Produce heat. Kinetic energy is the energy Of motion

9. The formula for kinetic energy Will be used often… KE = ½mv2

10. Problem... A 7 kg bowling ball moves at 3 m/s. How much kinetic energy does my Ball have? How fast must a Ping-pong ball (4.5) move to have The Same kinetic energy as the Other ball? 31.5 J 160 m/s

11. Problem... Calculate the KE of an 8.0 X 104 kg airliner Flying at 600 km/h. 1.1 X 109 J

12. The work-kinetic energy theorem Says that the net work done on An object is equal to the change In the kinetic energy of The object. The turns into a formula… W = ΔKE

13. PROBLEMS... A 105 g hockey puck is sliding Across the ice. Alec exerts a Constant 4.5 N force over a Distance of 0.15 m. How much Work is does Alec do on The puck? What is the change In the puck’s energy? 0.68 J

14. Power is the rate at which Energy is transferred. Or better stated as… W Δt P = Fv P = or

15. The SI unit for power is the Watt. A watt is defined as 1 J/s. Horsepower can also be used, And is equal to 746 W.

16. Problem... A 193 kg curtain needs to be raised 7.5m in as close to 5 s as possible. Three motors are available. The Power rating on each motor is 1 kW, 3.5 kW and 5.5 kW. Which Motor is best for the job. The 3.5 kW motor is best.

17. Problem... A 1000 kg elevator carries a Max load of 800 kg. A constant Frictional force of 4000N retards The motion. What minimum power Must the motor deliver to lift the Fully loaded elevator at a Constant speed of 3 m/s ? 66 kW

20. 10.2 Machines There are 6 different types of Simple machines. A lever and Fulcrum An inclined plane Wheel and axle Wedge Pulley Screw

21. Inclined Plane Wheel & Axle

22. Screw Wedge

23. Lever Pulley

24. The point of a machine is to Make work easier. The amount that the work Gets easy is called Mechanical Advantage.

25. Fout Fin Output Force Input Force MA = = IMA is the Ideal Mechanical Advantage de = distance exerted de dr IMA = dr = distance Of the object

26. Efficiency is a measure of How well a machine works. Wout Win MA IMA eff = eff = A gasoline car is only about 30% efficient, where as an electric Car is about 90% efficient!!

27. Problem... A bike wheel has a radius of 35.6 cm and a gear with radius of 4 cm. When the chain is pulled 155N The rim moves 14 cm. the efficiency Is 95%. What is the IMA? What Is the MA? What is the resistance Force? How far was the chain pulled? 0.112 0.106 16.4 1.57

28. THE END