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# Mechanical Comprehension Overview for ASVAB Power Practice Problems (page 2)

By LearningExpress Editors
LearningExpress, LLC
Updated on Aug 24, 2011

1. a.   w1 × d1 = w2 × d2. 27 pounds × 4 feet = 24 pounds × d2. Solving for d2 gives 4.5 feet.
2. b.   A pulley system of this type has a mechanical advantage of 3. If 160 pounds of force is applied, a maximum weight of 160 pounds × 3 = 480 pounds can be lifted.
3. c.   An object will float on top of a liquid if its density is less than the liquid it is in and sink if its density is greater. In this case, the penny is less dense than mercury and denser than water, so it will float on top of the mercury and sink in water, meaning it will settle directly in between the two layers.
4. a.   The mechanical advantage (MA) of a ramp is determined by the length of the ramp, l, divided by the height gained, h. In this case, MA = = 20 feet ÷ 5 feet = 4. The force required to pull a 240-pound block up a ramp is 240 pounds ÷ 4 = 60 pounds.
5. b.   Mechanical advantage = output force ÷ input force. Here, 50 pounds of force is input into a jack to lift a 3,000-pound car. The mechanical advantage is 3,000 ÷ 50 = 60.
6. a.   Heating leads to an increase in pressure of a contained gas. Since no air is added or removed from the tires, their overall weight remains constant.
7. b.   The arm acts as a lever with the pivot point being where it intersects the crane body. By attaching the cable as far along the arm as possible, the greatest mechanical advantage is achieved.
8. a.   The total weight of the block and the plank is 14 pounds. The weight is distributed evenly between the two scales, meaning that Scale 1 will read 7 pounds.
9. b.   The force constant of the spring is 9 pounds ÷ 3 inches = 3 pounds per inch. Using the equation, F = kx, we have 12 pounds = 3 pounds per inch × x. Solving for x gives 4 inches.
10. a.   An object's density determines whether it will float or sink. To float, it must have a lower density than water. Surface area will not affect whether an object ultimately floats or sinks.
11. b.   If 15 turns move the nut 1.25 inches, there are 15 turns ÷ 1.25 inches = 12 threads per inch.
12. b.   The mechanical advantage of this pulley system is 2. The force required to lift the 200-pound load is 200 pounds ÷ 2 = 100 pounds.
13. b.   Metals such as steel tend to expand considerably when heated. The other materials may expand somewhat when heated, but to a lesser extent.
14. c.   Each revolution of gear 1 will turn gear 2 12 teeth ÷ 9 teeth = times. At 30 revolutions per minute, gear 2 will turn at 30 rpm × = 40 rpm.
15. b.   The mechanical advantage (MA) of a ramp is determined by the length of the ramp, l, divided by the height gained, h. In this case, MA = = 18 feet ÷ 6 feet = 3. Since the barrel weighs 300 pounds, a force of 300 ÷ 3 = 100 pounds is required to keep the barrel in place.
16. c.   Each turn of the pedals will move the rear wheel 55 ÷ 11 = 5 revolutions. If the bike is pedaled at 80 rpm, the rear wheel will rotate at 80 rpm × 5 revolutions = 400 rpm. Since 30 seconds is half of one minute, the rear wheel will complete 400 rpm ÷ 2 = 200 revolutions
17. a.   Helium is less dense than air. Objects will float when they are less dense than air. Helium will float regardless of its temperature.
18. c.   While no mechanical advantage is gained, a pulley system such as this one allows one to raise an object while pulling downward, rather than having to climb above the object to pull it.
19. d.   If gear 4 turns clockwise, the neighboring gears 1 and 3 will turn counterclockwise.
20. d.   The amount of water that flows out through the pipes is proportional to the size of the pipe opening. Since the area of the opening is proportional to the square of the diameter, the ratio of the amount of water that flows out of A and B is 62 ÷ 22 = 9.
21. c.   14 miles ÷ 8 mph = 1.75 hours = 1 hour 45 minutes.
22. c.   If the 600-pound block can be lifted with 200 pounds of force, the ramp has a mechanical advantage (MA) of 3. The MA of a ramp is determined by the length of the ramp, l, divided by the height gained, h. In this case, . Solving for h tells us the ramp is 5 feet high.
23. a.   w1 × d1 = w2 × d2. Paul is 15 feet away from the pivot point and the block is 20 feet away. 90 × 20 feet = 15 feet × w2. Solving for w2 gives 120 pounds.
24. c.   As the balloon rises, the air pressure surrounding it will decrease and the internal pressure from the helium will press outward on the walls of the balloon, increasing it in size. Since the balloon is a closed system, its weight will be unaffected.
25. d.   Since pulley A is 1.5 times greater in circumference than pulley B, each revolution of A will lead to 1.5 revolutions of B. The belt of the pulley will cause pulley B to move in the same direction (counterclockwise) as pulley A.

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