Practice sheet for Science Exam - Ms. Ziliotto King Edward ...



Practice sheet for Science Exam

1. How does friction affect the efficiency of a system?

2. Calculate the mechanical advantage of a wheelbarrow if the effort force is 250 N and the load force is 750 N.

3. Calculate the M.A. of the gear train if the effort force is 100 N and the load force is 1000N.

4. List three ways a machine makes things easier for us.

5. Classify each of the following as a Class 1, Class 2 or Class 3 lever:

a. Broom

b. Bottle opener

c. Seesaw

d. Fly swatter

e. Nutcracker

6. What would be the M.A. of a lever that can lift 80 N with an effort of only 20N?

7. In order to lift a load a distance of 6 m by a pulley, it is necessary to move the effort load by 3 m. What would be the velocity ratio?

8. A single movable pulley is being used to lift a 135 N object by using 75 N of effort. What is the M.A.?

9. You use a single movable pulley to lift an object weighing 1000N. You apply an effort of exactly 500N. Will the object lift?

10. A wheel and axle system has a mechanical advantage of 4. The effort used is 12 N. What is the maximum load force that can be moved, assuming there is no friction?

11. “A machine that requires more effort to lift an object than the load itself is useless.” Explain why you think this statement is true or false.

12. How much work, in joules, must you do to lift an elephant weighting 60 000 N up 1.5 m onto the back of a truck?

13. You have found a ramp to lead up to the back of the truck. If the slope of the ramp is 18 m long, how much force (in newtons) will you and your team need to exert to move the 60 000 N elephant up the ramp?

14. If you exert a force of 100 N on a hockey stick, and the stick exerts a force of 20 N on the puck, what is the mechanical advantage of the stick?

15. If the effort arm distance for the hockey stick in the last question is 25 cm, how long is the stick?

16. Sketch a lever that has a mechanical advantage of 1.

17. If the chain of your bicycle is running from the largest front sprocket to the smallest back sprocket, are you in high gear or low gear? Would you use this gear while pedaling up a steep hill or cruising fast on a level road? Explain.

18. A gear with a 9 cm radius is turning another gear that has a radius of 3 cm. What is the M.A.?

19. Distinguish between a single fixed and a single movable pulley and describe the advantages of each.

20. State at least three situations in which it would be more practical to use a wheel and axle rather than a lever.

21. Sketch a diagram showing how you could use one single pulley and one double pulley to gain a mechanical advantage of 3.

22. Which does not describe what a machine does?

a. Changes the effort force

b. Transforms Newtons

c. Changes the direction of a force

d. Does work

23. Two ramps of different lengths are used to lift furniture into the same truck. Which ramp requires less force?

24. A metre stick is used as a lever. If the input force is applied at 0 cm, and the output force is exerted at 100cm, what is the ideal mechanical advantage if the fulcrum is at 75 cm?

25. A student does 25 J of work on the handle of a pencil sharpener. If the pencil sharpener does 20 J of work on the pencil, what is the efficiency of the sharpener?

26. For which class(es) of lever(s) are the input force and the output force in the same direction? Opposite direction?

27. How does the output work compare to the input work for a machine that has an efficiency

a. Equal to 100%

b. Less than 100%

28. To increase the mechanical advantage of a lever, should you increase or decrease the length of the output arm?

29. What is the M.A. of a lever whose input force is applied 3 m from the fulcrum and whose output force is 0.5 m from the fulcrum?

30. A ramp is 5 m long is used to raise an object 2 m vertically. What is the M.A.?

31. The handle of a screwdriver has a radius of 3 cm. If the shaft of the screwdriver has a radius of 0.5 cm, what is the M.A. of the screwdriver when used to tighten a screw?

32. Wei uses a pulley system to lift a box. She pulls the rope a distance of 3m, the load moves a total of 1m, what is the velocity ratio?

33. In Canada, our government is considered a “democratic system”. Is this a mechanical or a non-mechanical system? Explain.

34. What factors affect the evolution of a system?

35. The radius of a screw is 3 cm and the pitch of the screw is 1/5 (meaning there are 5 threads per cm). What is the mechanical advantage of the screw?

36. If a driver gear has 25 teeth and the follower gear has 50 teeth, what is the gear ratio?

37. What is the mechanical advantage of the three pulley systems below:

[pic]

38. What is the gear ratio of the following gear systems:

39. Draw a diagram of each lever class. In each case, place the fulcrum, the load and the effort force in positions that will give you the best mechanical advantage in each case.

40. Are you ready for this exam?

Answers:

1. It reduces efficency

2. M.A. = 3

3. M.A. = 10

4. Changes direction of force, reduces effort force, increase or decrease speed

5. Levers are:

a. 3rd

b. 2nd

c. 1st

d. 3rd

e. 2nd

6. M.A. = 4

7. V.R. = 1:2

8. M.A. = 1.8

9. M.A. = 2; yes

10. Load = 48 N

11. False, because it can change the direction of the force or/and it might gain distance rather than decrease force.

12. W = 90 000N

13. F = 5000 N

14. M.A. = 0.2

15. 125 cm

16. It should look like a see saw; equal distance from the load to fulcrum and effort to fulcrum

17. Low gear, downhill or flat surface

18. M.A. = 0.3333

19. Single Fixed changes direction, single movable M.A. = 2

20. Any scenario you might need the lever to rotate 360o

21. (ask me if you’re not sure)

22. Transforms Newtons

23. The one that is larger

24. M.A. = 3

25. M.E.= 80%

26. 2nd and 3rd

27. a) Output and input are equal b) Input is larger than output

28. Decrease the output arm

29. M.A.=6

30. M.A. = 2.5

31. M.A.=6

32. 3:1

33. Non-mechanical system

34. Efficiency, safety, cost and environmental impact

35. M.A. = 94.2

36. 2:1

37. 1, 2, 4

38. 2:1

39. (ask me if your not sure)

40. Yes!!!

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