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Chapter 5 Study Guide

Chapter 5 Study Guide. 1. _____ is a transfer of energy that occurs when a force makes an object move. Answer: Work 2. The rate at which work is done is___. Answer: Power 3. ______is transferred to an object when work is done. Answer: Energy

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Chapter 5 Study Guide

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  1. Chapter 5 Study Guide 1. _____ is a transfer of energy that occurs when a force makes an object move. Answer: Work 2. The rate at which work is done is___. Answer: Power 3. ______is transferred to an object when work is done. Answer: Energy 4. A device that does work with only one movement is a ____. Answer: Simple machines

  2. 5. Machines can make work easier in what three ways? Answer: change the size of the effort force, change the direction of the effort force or increase the distance over which the force is applied. 6. A compound machine is____. Answer: Two or more machines that work together. 7. The six simple machines are____. Answer: Inclined plane, wedge, screw, lever, pulley & wheel and axle. 8. An inclined plane wrapped around a cylindrical post is _____. Answer: a screw. (Examples – screw, jar lid, nut & bolt) 9. A slanted surface used to raise an object is___. Answer: Inclined plane. (Examples – ramp, mountain)

  3. 10. Two inclined planes put together is____. Answer: Wedge (Examples – saw, axe, zipper teeth, 11. A bar that is free to pivot about a fixed point is ___. Answer: Lever (Examples – screwdriver, crowbar, tweezers, tongs, nutcracker, see-saw, baseball bat, wheelbarrow, scissors) 12. A grooved wheel with a rope, chain or cable running along it is___. Answer: Pulley (Examples – farris wheel, window shade or blinds, flagpole) 13. Name the three types of pulleys and how they make work easier. Answer: fixed – change the direction of the effort force; movable – multiply the effort force; block and tackle – multiply the effort force. 14. Two wheels of different sizes that rotate together are____. Answer: Wheel and Axle (Examples – bicycle, door knob, hand crank, steering wheel)

  4. 15. Efficiency is ___. Answer: The work output compared to the work input. 16. Mechanical Advantage is ___. Answer: The number of times the machine multiplies the effort force. 17. If there is no friction involved and a force of 25 N is exerted over a distance of 4m to move a 5N object, how far will the object be moved? Answer: If there’s no friction then Woutput = Winput so, Fr x dr = Fe x de ( 5N ) dr = (25N) x (4m) (5N) (5N) dr = 20m 18. How much work is done if 500N of force is applied to an object that remains stationary? Answer: ZERO

  5. 19. What kind of simple machine is this and what type? Answer: pulley – single fixed 20. What is the mechanical advantage? Answer: 1 21. How does it make work easier? Answer: it changes the direction of the effort force 22. If a person applies a force of 20N to pry open a wooden crate that has a resistance of 500N, what is the mechanical advantage? Answer: AMA = RF/EF AMA = 500N/20N AMA = 25

  6. 23. What is the IMA of this simple machine if A = 2m, B = 8m and C = 10m? (Remember the length of the ramp is the de and the height of the ramp is the dr ). Answer: IMA = de/dr IMA = 10m/2m IMA = 5 *You do not need the length of segment B. 24. What is the efficiency of this machine if its MA = 4 and its IMA = 6? Answer: Eff = MA / IMA x 100% Eff = 4 / 6 x 100% = 66.7% 25. How are inclined planes, screws and wedges related? Answer: Wedges are two inclined planes put back-to-back and a screw is an inclined plane wrapped around a cylindrical post.

  7. 26. What is one way that you could reduce the amount of work lost to friction in a machine? Answer: add a lubricant like oil or WD-40. 27. How would that affect the machines efficiency? Answer: its efficiency would increase because less work would be lost to friction. 28. How would work of walking up a flight of stairs compare to the work of running up the same flight of stairs? Answer: they would be the same. 29. How would the power compare in each situation? Answer: The power of running up the stairs would be MORE than the power of walking up the stairs.

  8. 30. Calculate the amount of work done when a force of 600N moves an object a distance of 4m. Answer: W = Fxd W = 600N x 4m W = 2400J 31. If 300J of work is done to lift a 150N object, how far was the object moved? Answer: W = Fxd 300J = 150N x d d = 2m

  9. 32. Calculate the amount of power used to do 700J of work in 20 sec. Answer: P = W/t P = 700J/20s P = 35 Watts 33. If a person uses 1000 Watts of power to push a 500N box across the floor in 2sec, how far does he move the box? Answer: P = W/t 1000 w = W / 2s W = 500J W = Fxd 500J = 500N x d d = 1m

  10. 34. A student takes 20 sec to push a basket a distance of 40 m. How much force was exerted if 100 Watts of power was used? Answer: P = W/t 100 w = W / 20s W = 2000J W = Fxd 2000J = F x 40m F = 50N 35. If a lever has a mechanical advantage of 10, how much force must be exerted to move a 5000N object? Answer: AMA = Fr/Fe 10 = 5000/Fe Fe = 500N

  11. 36. If a lever has a mechanical advantage of 8 and an effort force of 20N is used, how heavy of an object can be moved? Answer: AMA = Fr/Fe 8 = Fr / 20N Fr = 160 N 37. A machine has an efficiency of 70%. If the work input is 1000J, what is the work output? Answer: Efficiency = Wout / Win .70 = Wout / 1000J Wout = 700J ***Don’t forget to put your efficiency as a percentage!

  12. 38. If 5000J of work is put into a machine and 1500J are lost to friction, what is the work output by the machine and the efficiency? Answer: Woutput = Winput – W lost to friction Wout = 5000J – 1500J = 3500J Efficiency = Wout / Win x 100 Efficiency = (3500J / 5000J) x100 Efficiency = .70 x 100 Efficiency = 70%

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