ASVAB Mechanical Comprehension Practice Test: Pressure, Fluids, Springs and Structures
- Pressure, Fluids, Springs and Structures
- 15 questions
- 18 minutes
These questions cover pressure and hydraulics, liquids in tanks and pipes, floating objects, springs and how loads spread through beams and frames. Tip: pressure is force divided by area, so the same force on a smaller area gives more pressure.
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Question 1
A force of 600 lb is spread evenly over an area of 20 square inches. What is the pressure?
Correct answer: C
Pressure = force ÷ area = 600 ÷ 20 = 30 pounds per square inch (psi). 12,000 comes from multiplying instead of dividing.
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Question 2
In a hydraulic jack, the small piston has an area of 2 square inches and the large piston has an area of 40 square inches. A 50-lb force on the small piston can lift how much on the large piston?
Correct answer: A
The pressure under the small piston is 50 ÷ 2 = 25 psi. The same pressure acts on the large piston: 25 × 40 = 1,000 lb.
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Question 3
In the same jack (small piston 2 sq in, large piston 40 sq in), the small piston is pushed down 10 inches. How far does the large piston rise?
Correct answer: D
The volume of fluid pushed out of the small cylinder (2 × 10 = 20 cubic inches) enters the large cylinder: 20 ÷ 40 = 0.5 inch. The jack gains force but gives up distance.
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Question 4
Pascal's principle says that pressure applied to a confined liquid
Correct answer: B
Pressure applied to a liquid in a closed system is passed on undiminished in every direction. Hydraulic brakes and jacks depend on this.
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Question 5
A tall tank full of water has three small holes of the same size: one near the top, one in the middle and one near the bottom. From which hole does water spray out with the greatest force?
Correct answer: A
Water pressure increases with depth, because more water is pressing down from above. The bottom hole has the most water above it, so the stream there is strongest.
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Question 6
Water flows at 3 ft per second through a pipe with a 4-inch inside diameter. The pipe narrows to a 2-inch diameter. How fast does the water flow in the narrow section?
Correct answer: C
Halving the diameter makes the cross-section area one-fourth as large (area depends on diameter squared), so the same amount of water must move 4 times as fast: 3 × 4 = 12 ft/s. 6 ft/s forgets to square the diameter ratio.
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Question 7
A wooden block that weighs 30 lb floats at rest in a lake. How large is the buoyant force on the block?
Correct answer: D
A floating object is in balance: the upward buoyant force equals its weight, 30 lb. If the buoyant force were smaller the block would sink; if it were larger the block would rise.
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Question 8
A spring stretches 2 inches when a 10-lb weight hangs from it. How far will it stretch with a 25-lb weight?
Correct answer: B
Within its limit a spring stretches in proportion to the load: 10 lb gives 2 inches, so each pound gives 0.2 inch, and 25 × 0.2 = 5 inches.
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Question 9
A single spring stretches 1 inch under a 10-lb load. Two of these springs are hooked end to end (one below the other), and the same 10-lb load hangs from the bottom. How far does the pair stretch in total?
Correct answer: B
In series each spring carries the full 10 lb, so each stretches 1 inch and the total is 2 inches. Side-by-side springs would share the load instead.
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Question 10
A single spring stretches 1 inch under a 10-lb load. Two of these springs hang side by side and hold up one 10-lb load together. How far does each spring stretch?
Correct answer: D
Springs in parallel share the load: each carries 5 lb, and half the load gives half the stretch, 0.5 inch.
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Question 11
A uniform 10-ft beam rests on a support at each end. An 800-lb load hangs exactly in the middle. Ignoring the beam's own weight, how much does each support carry?
Correct answer: C
With the load in the center, the two supports share it equally: 800 ÷ 2 = 400 lb each.
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Question 12
A 10-ft beam rests on supports L and R at its ends. A 600-lb load is placed 2 ft from support L.
Ignoring the beam's weight, how much of the load does support L carry?
Correct answer: A
The support nearer the load carries more. Each support's share is the load times the distance to the other support, divided by the beam length: L carries 600 × 8 ÷ 10 = 480 lb, and R carries the remaining 120 lb.
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Question 13
Builders add diagonal braces to a rectangular frame mainly because
Correct answer: D
A rectangle can lean into a parallelogram without any side getting longer or shorter, but a triangle cannot. A diagonal splits the rectangle into two triangles and makes it rigid.
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Question 14
Why do car brake systems use a liquid (brake fluid) instead of air to transmit force?
Correct answer: B
A liquid hardly changes volume under pressure, so pushing the pedal moves the brake pistons right away. Air would compress, and the pedal would feel soft and travel too far.
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Question 15
A horizontal beam supported at both ends bends slightly downward under a heavy load in the middle. Which part of the beam is being stretched (in tension)?
Correct answer: A
When the beam sags, its lower surface gets longer and is pulled (tension), while its upper surface is squeezed (compression). That is why steel bars in concrete beams are placed near the bottom.
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