Chapter 12 SG Review 8 th - Advanced

1. Define Work – When you exert force on an object and it causes an object to move some distance. 2. When is work done. – When an object moves a distance. 3. To do work what direction does the motion have to be? – Parallel to the direction of the force applied. 4. What is the equation for work? – Work = force x Distance 5. What is the unit for work? – Joules

6. Define power? – Amount of work done in a unit of time. 7. What is the equation for power? – Power = work/time 8. What is the unit for power? – Watts 9. What is a machine? – A device that makes work easier. 10. What are 3 ways in which a machine makes work easier? – 1) changes the amt of force you exert 2) changes the distance over which you exert a force 3) changes the direction in which you exert the force

11. What is input force? – The force you exert on the machine. 12. what is an output force? – The force the machine exerts on an object 13. What is input work? – Input force X input distance 14. What is output work? – Output force X output distance 15. If the amount of work stays the same a decrease in force means a(n) ________ in distance. – Increase

16. What happens if output force is less than input force? – Mechanical advantage would be less than What is mechanical advantage? – The number of times a machine increases a force exerted on it. 18. How do you calculate mechanical advantage? – Output force/ input force 19. What force always causes some work to be wasted? – Friction

20. What is efficiency? – Expressed as a percent and compares the output work to the input work. 21. Why is output always less than input in real situations? – In every machine, some work is wasted overcoming the force of friction. 22. How do you calculate efficiency? – Efficiency = output work/ input work x 100% 23. What is a machines ideal mechanical advantage? – Output force/ input force (IDEAL= NO FRICTION)

24. What does 1 horsepower equal? – 745 watts 25. What are the 6 basic types of machines? – 1) wheel and axle 2) inclined plane 3) screw – 4) lever 5) pulley 6) wedge 26. As the length of the incline plane increases what happens to your input force? – It decreases 27. What are 5 examples of wedges? – 1) front two teeth 2) door stopper 3) wedge heel of your shoe 4) scissors 5) end of an ax

28. What is a screw? – An inclined plane wrapped around a cylinder 29. What is a lever? – A rigid bar that is free to pivot, or rotate, on a fixed point 30. What is a fulcrum? – The fixed point that a lever pivots around. 31. How many different types of levers are there? How are they classified? – 3 Different types of levers – Levers are classified according to the location of the fulcrum relative to the input and output forces.

32. How do you determine the mechanical advantage of a pulley system? – The ideal mechanical advantage of a pulley is equal to the number of sections of rope that support the object. 33. Joe applies 250N force to move a bolder 40m, how much work did Joe do? – W = F x D – W= 250 x 40 = 10,000J 34. How far will 100 J raise a 2Kg mass? – W = F x D – 100 J = 2(9.8 m/s2) x D – 5.1 Meters

35. How much power does it take to do 104J of work in 8 seconds? – P = work/ time – P= 104J/ 8 Seconds – P= 13 Watts 36. How much power does it take to lift 50 N 20 m in 10 seconds – P = (F x D)/ time – P= (50N x 20m) / 10seconds – P = 100 Watts

37. If a motor uses 1500J of energy to raise 10Kg 10m high, what is the efficiency of the motor – F = ma – F= 10kg (9.8)= 98 N – W= F x D – W= 98N x 10M= 980J – Efficiency = (output work/ input work) x 100% – E = (980/ 1500) x 100 = 65%

38. A 300 watt electrical motor takes 10 seconds to raise 5 kg 40 m. What is the efficiency of the motor. – F = ma – F= 5kg x 9.8 = 49N – W= F x D – W = 49n x 40m= 1960J – P= W/Time – P= 1960J / 10sec = 196 Watts – Efficiency = output/input x 100 – Efficiency = (196/300) x 100 = 65%

39. What is the efficiency of a block and tackle if a 60 kg mass pulls 30m of rope to a raise 500kg piano 2m. – Efficiency = output work / input work x 100 – First you can to calculate the work – Before you can do that you have to calculate the force of each. – F = ma, w = F x D – E = (500kg (9.8) x 2m)/ (60kg (9.8) x 30m) x 100% – E = 55%