ASVAB Mechanical Comprehension Practice Test: Force, Work, Inclined Planes and Screws
- Force, Work, Inclined Planes and Screws
- 10 questions
- 12 minutes
This test covers forces and motion and the simple machines not built from levers or gears: the inclined plane, the wedge and the screw. Unless a question says otherwise, ignore friction.
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Question 1
A ramp is 12 feet long and rises 3 feet. Ignoring friction, how much force is needed to push a 200-pound load up the ramp?
Correct answer: D
The mechanical advantage of the ramp is length ÷ height = 12 ÷ 3 = 4, so the force is 200 ÷ 4 = 50 pounds. The answer 800 multiplies by the advantage instead of dividing.
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Question 2
How much work is done in lifting a 150-pound crate straight up 4 feet?
Correct answer: C
Work equals force times distance: 150 × 4 = 600 foot-pounds. Dividing gives 37.5, and adding gives 154; neither is work.
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Question 3
A hoist lifts a 500-pound load 10 feet in 5 seconds. How much power does it deliver?
Correct answer: A
Work is 500 × 10 = 5,000 foot-pounds, and power is work ÷ time = 5,000 ÷ 5 = 1,000 foot-pounds per second. Multiplying by the time instead of dividing gives 25,000.
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Question 4
A bolt has 8 threads per inch. How many full turns are needed to drive it 1.5 inches into a threaded hole?
Correct answer: B
Each turn advances the bolt one thread, or 1/8 inch. To move 1.5 inches it needs 1.5 × 8 = 12 turns.
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Question 5
Two ramps lead up to the same loading dock. Ramp X is twice as long as ramp Y. Ignoring friction, pushing a crate up ramp X instead of ramp Y takes
Correct answer: B
A longer ramp is less steep, so it takes less force, but the crate must be pushed farther. Without friction the total work is the same on both ramps, so "less work" is wrong.
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Question 6
When an axe splits a log, the blade acts as a wedge. A wedge works by
Correct answer: D
The sloped sides of a wedge change the downward blow into forces that push the two halves of the log apart. It does not store energy like a spring.
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Question 7
Four identical trucks carry the same weight of cargo. Which truck is most likely to tip over in a sharp turn?
Correct answer: C
Stacking cargo high raises the center of gravity, which makes a vehicle easier to tip in a turn. The other three keep the weight low.
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Question 8
Ball bearings in a wheel hub reduce friction mainly because they
Correct answer: A
Rolling friction is much smaller than sliding friction, so balls rolling between the hub and axle let the wheel turn easily. A rougher surface would increase friction.
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Question 9
A passenger standing in a bus falls forward when the bus stops suddenly. This happens because of
Correct answer: A
Inertia is the tendency of a moving body to keep moving. The bus stops, but the passenger's body keeps going forward until something stops it.
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Question 10
A worker pushes a box east with a force of 30 pounds. Friction acts on the box with a force of 12 pounds toward the west. What is the net force on the box?
Correct answer: D
Forces in opposite directions subtract: 30 − 12 = 18 pounds, in the direction of the larger force, east. Adding them to get 42 would be correct only if both acted in the same direction.
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