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

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Updated on Aug 12, 2011

1. c.   The mechanical advantage of this pulley system is 2. The force required to lift the 276 pound load is 276 pounds ÷ 2 = 138 pounds.
2. d.   Valves 3 and 4 allow liquid from tank A to flow to the outlet, while opening 2 provides a direct route for liquid to travel from C to A.
3. d.   When water freezes into ice, it expands, meaning that it becomes less dense than water. Objects that are less dense than the fluid they are in will float.
4. a.   w1 × d1 = w2 × d2. Shannon is 20 feet away from the pivot point. 100 pounds × 9 feet = 20 feet × w2. Solving for w2 gives 45 pounds.
5. c.   For every 1 rotation of gear 2, gear 1 turns 9 teeth ÷ 12 teeth = times. If gear 2 turns at 60 rpm, then gear 1 will turn at 60 rpm = 45 rpm.
6. c.   w1 × d1 = w2 × d2. The crane shown is a special type of lever. The weight is 16 feet away from the pivot point, and the lifting cable is 10 feet from the pivot point. 600 pounds 16 feet = 10 feet × w2. Solving for w2 gives 960 pounds.
7. 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 = = 24 feet ÷ 6 feet = 4. The force required to pull a 500-pound block up a ramp is 500 pounds ÷ 4 = 125 pounds.
8. c.   When Alex departs, Jill is 40 miles ahead. After 1 hour, Alex has traveled 60 miles and Jill 80 miles. After 2 hours, both Alex and Jill will have traveled 120 miles.
9. a.   Since the circumference of B is twice that of A, A will have to complete 2 revolutions per 1 revolution of B. Therefore, B must rotate at 10 rpm.
10. c.   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 2.5 pounds per inch a distance of 10 inches is 2.5 × 10 = 25 pounds.
11. a.   Styrofoam is an excellent insulator, meaning that it prevents heat from flowing from the coffee to the surrounding environment. It also keeps one's hands from being burned by hot coffee.
12. d.   The nut will move 1 inch down the screw every 20 turns. To travel 1.5 inches, the nut must be turned 1.5 inches × 20 turns per inch = 30 turns.
13. a.   Oil is less dense than water. When two immiscible liquids of different density combine, the one that is less dense will always float to the top.
14. c.   The 6-pound weight will compress the first spring: 6 pounds ÷ 2 pounds per inch = 3 inches. The second spring compresses 6 pounds ÷ 3 pounds per inch = 2 inches. The third spring compresses 6 pounds ÷ 6 pounds per inch = 1 inch. The total amount the platform compresses is therefore 3 + 2 + 1 = 6 inches.
15. b.   w1 d1 = w2 d2. 180 pounds × 4 feet = w2 × 9 feet. Solving for w2 gives 80 pounds.
16. b.   A pulley system of this type has a mechanical advantage of 2. So, lifting a 200-pound weight will require 200 pounds ÷ 2 = 100 pounds.
17. c.   An ax head is a wedge used to split a piece of wood. It can be thought of as two ramps pressed together.
18. c.   In this pulley system, the weight of the box is shared by 3 cables. So, it will have a mechanical advantage of 3.
19. b.   If gear 1 turns clockwise, it will cause gear 2 to turn counterclockwise, and gear 3 will turn clockwise.
20. c.   Mechanical advantage (MA) is the factor by which a simple machine multiplies for the force put into it. In this case, 50 pounds of force is used to move a 200-pound block, so MA = 200 ÷ 50 = 4. The MA of a ramp is determined by the length of the ramp, l, divided by the height gained, h. In this case, MA = 4 = = feet. Solving for l tells us the ramp is 40 feet long.
21. b.   Each full turn of the pedals will turn the rear wheel 48 ÷ 16 = 3 revolutions. 3 turns of the pedals will turn the rear wheel 3 × 3 = 9 revolutions.
22. b.   Combustion creates a dense, high-pressure gas that rapidly expands and pushes the piston downward.
23. b.   Metal boat anchors offer the advantages of being dense and strong.
24. d.   w1 × d1 = w2 × d2. 85 pounds × 9 feet = 45 pounds. d2. Solving for d2 gives 17 feet.
25. a.   For the 16-tooth cog, the bike travels 48 ÷ 12 = 4 revolutions per pedal stroke, and 48 ÷ 16 = 3 revolutions per pedal stroke for the 12-tooth cog. At 80 turns of the pedal per minute, the bike wheel completes 80 × 3 = 240 rpm. In order to match that speed using the 12-tooth cog, one must pedal 240 rpm ÷ 4 = 60 rpm.