ASVAB Mechanical Comprehension Practice Test: Wheel and Axle, Momentum and Rotating Parts
- Wheel and Axle, Momentum and Rotating Parts
- 10 questions
- 15 minutes
These questions cover rotating machines, motion and how materials react to heat. For wheel and axle problems, compare the two radii: the larger one always moves farther with less force.
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Question 1
A wheel with a radius of 12 inches is fixed to an axle with a radius of 2 inches. A rope wound on the axle holds a 300-lb load. Ignoring friction, what force on the rim of the wheel will hold the load?
Correct answer: C
The mechanical advantage is 12 ÷ 2 = 6, so the force is 300 ÷ 6 = 50 lb. The answer 1,800 lb multiplies by 6 instead of dividing.
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Question 2
A water valve with a small handle is hard to turn. A worker replaces it with a handle twice as wide. Why is the valve now easier to turn?
Correct answer: A
Torque equals force times distance from the center, so a wider handle gives more turning effect for the same push. The friction inside the valve is unchanged.
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Question 3
A 1,500-kilogram car moves at 20 meters per second. What is its momentum? (Momentum = mass × velocity)
Correct answer: D
1,500 × 20 = 30,000 kg·m/s. The answer 75 divides mass by velocity instead of multiplying.
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Question 4
A 2-kilogram cart rolling at 3 meters per second hits a 1-kilogram cart that is standing still. The carts lock together and roll on. Ignoring friction, how fast do they move?
Correct answer: B
Momentum is conserved: 2 × 3 = 6 kg·m/s before, shared by 3 kg after, so 6 ÷ 3 = 2 m/s. The answer 6 is the momentum, not the speed.
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Question 5
A bicycle wheel spins at a steady rate. Which point on the wheel moves at the greatest speed?
Correct answer: C
Every point makes one turn in the same time, but a point on the rim travels the largest circle, so it moves fastest. All points share the same rotation rate, not the same speed.
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Question 6
A cam is fixed to a rotating shaft, and a follower rests on the cam's edge. What kind of motion does the cam give to the follower?
Correct answer: A
A cam changes rotating motion into back-and-forth motion, as when it opens and closes engine valves. Changing rotation speed or direction is the job of gears.
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Question 7
A heavy flywheel is attached to the shaft of an engine. What is its main purpose?
Correct answer: D
A spinning flywheel stores energy and resists changes in speed, which smooths out the uneven pushes of the pistons. It adds weight rather than reducing it.
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Question 8
Concrete sidewalks are poured in sections with narrow gaps between them. What is the main reason for the gaps?
Correct answer: B
Materials expand when they warm and shrink when they cool, so the joints give the slabs room to move. Without them, the pressure would crack the concrete.
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Question 9
A metal lid is stuck on a glass jar. Holding the lid under hot water often loosens it. Why?
Correct answer: C
Metal expands more than glass for the same temperature rise, so the lid grows slightly larger than the rim of the jar. Glass expands a little when heated; it does not shrink.
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Question 10
A 1-lb steel ball and a 10-lb steel ball are dropped at the same moment from the same height. Ignoring air resistance, which statement is true?
Correct answer: A
Without air resistance, gravity gives all objects the same acceleration, so they fall together. A heavier object is pulled harder, but it also needs more force to speed up.
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