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

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1. c.   The 20-pound block is located closer to scale 1 than scale 2. Scale 1 will support more than half the weight of the block.
2. c.   w1 × d1 = w2 × d2.Todd is 6 feet away from the pivot point, and the block is 18 feet away. 50 × 18 feet = 6 feet × w2. Solving for w2 gives 150 pounds.
3. b.   When air is heated it expands and becomes less dense than cold air, making the entire balloon buoyant and allowing it to float.
4. d.   Mechanical advantage describes the factor that force is multiplied by a simple machine. Here, by moving the screw handle 3 feet , the jack is raised inch. Thus the mechanical advantage of the jack is 36 ÷ = 144.
5. d.   A pulley system of this type has a mechanical advantage of 4. So, if Bryan can pull a rope with 150 pounds of force, he will be able to lift a weight of 150 pounds × 4 = 600 pounds.
6. d.   Mechanical advantage = output force ÷ input force. Here, 20 pounds of force is input to lift 80 pounds of dirt. The mechanical advantage is 80 ÷ 20 = 4.
7. a.   Mechanical advantage (MA) is the factor by which a simple machine multiplies for the force put into it. In this case, 120 pounds of force is used to move a 360-pound block, so MA = 360 ÷ 120 = 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 l tells us the ramp is 30 feet long.
8. d.   The force required to stretch a spring is equal to its force constant multiplied by the distance stretch (F = kx). The force required to move a spring with a force constant of 3 pounds per inch a distance of 12 inches is 3 × 12 = 36 pounds.
9. d.   Since pulley A is three times greater in diameter than pulley A, each revolution of A will lead to 3 revolutions of B. If A rotates at 45 rpm, then B will rotate at 45 rpm × 3 = 135 rpm.
10. d.   Friction is the force that must be overcome in order to slide on object across another.
11. b.   There are 6 threads per inch. To move the nut 2 inches will require 6 × 2 = 12 turns.
12. c.   Water pressure at the bottom of a tank increases as the weight of water above it increases, but pressure at the top remains the same, since it has a finite amount of water above it.
13. a.   The entire weight is supported by a single cable and no mechanical advantage is achieved using this pulley system. So the mechanical advantage is 1.
14. c.   All other materials are denser than water and will sink. Styrofoam is not very dense and will float on water.
15. c.   Gear 1 turning clockwise will cause gear 2 to turn counterclockwise. In turn, this counterclockwise movement will cause gears 3 and 4 to turn clockwise.
16. d.   The 200-pound weight will stretch the first spring 200 pounds ÷ 400 pounds per inch = 0.5 inches. The second spring stretches 200 pounds ÷ 200 pounds per inch = 1 inch. The third spring stretches 200 pounds ÷ 100 pounds per inch = 2 inches. The total amount the platform compresses is therefore 0.5 + 1 + 2 = 3.5 inches.
17. d.   Since the two are traveling in opposite directions, the rate at which they move farther apart is equal to the sum of their two speeds (35 mph + 45 mph = 80 mph). After 2 hours, the two will be 80 mph × 2 hours = 160 miles.
18. b.   The first bike has 12 teeth on its rear cog and 52 teeth on front chain ring. At 60 rpm, the bike will travel 60 rpm × 52 front teeth ÷ 12 rear teeth = 260 revolutions. For the bicycle with 14 teeth on its rear cog to travel 260 revolutions, it must be pedaled at 260 revolutions × 14 teeth ÷ 52 front teeth = 70 rpm.
19. b.   If the container is being filled at 18 gallons per minute (gpm) and evacuated at 14 gpm, then it is filling at an overall rate of (18 – 14 = 4 gpm). Since the tank can hold 20 gallons, it will fill in 20 gallons ÷ 4 gallons per minute = 5 minutes.
20. a.   w1 × d1 = w2 × d2. 96 pounds × 5 feet =w2 × 12 feet. Solving for w2 gives 40 pounds.
21. 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, . The force required to pull a 800-pound block up a ramp is 800 pounds ÷ 5 = 160 pounds.
22. d.   Every full turn of the larger gear will result in 18 teeth ÷ 12 teeth = 1.5 rotations. In two turns of the larger gear, the smaller will complete 3 rotations.
23. a.   The lip of the paint can acts as a fulcrum of a lever when trying to pry off a lid. The long arm of a screwdriver provides a sizeable mechanical advantage.
24. a.   w1 × d1 = w2 × d2. Stevi is 14 feet away from the pivot point. 70 pounds × 9 feet = 14 feet × w2. Solving for w2 gives 45 pounds.
25. c.   A pulley system of this type has a mechanical advantage of 2. So, to lift a 150-pound weight will require 150 pounds ÷ 2 = 75 pounds.

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