ASVAB Mechanical Comprehension Practice Test: Levers, Pulleys and Gears
- Levers, Pulleys and Gears
- 15 questions
- 18 minutes
This test covers simple machines that trade force for distance: levers, pulleys, gears, belt drives and the wheel and axle. Ignore friction unless a question says otherwise. Tip: for gears, more teeth means slower turning, and each new gear in a chain reverses the direction.
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Question 1
A 40-lb weight sits on a lever 2 ft from the fulcrum. The effort is applied 8 ft from the fulcrum on the other side.
How much effort is needed to balance the weight?
Correct answer: B
Balance means weight × its distance = effort × its distance: 40 × 2 = effort × 8, so the effort is 80 ÷ 8 = 10 lb. Multiplying 40 by 4 (160 lb) is the trap: the longer arm reduces the force.
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Question 2
A wheelbarrow is an example of which class of lever?
Correct answer: C
The wheel is the fulcrum, the load sits in the middle, and you lift at the handles: load between fulcrum and effort is a second-class lever. In a first-class lever (a seesaw) the fulcrum is in the middle.
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Question 3
Which tool works as a third-class lever, with the effort applied between the fulcrum and the load?
Correct answer: A
Tweezers are hinged at one end, you squeeze in the middle and the tips hold the load, so the effort is between fulcrum and load. A nutcracker has the load in the middle (second class); a seesaw and a crowbar used over a block are first-class levers.
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Question 4
A lever has an effort arm 6 ft long and a load arm 1.5 ft long. What is its mechanical advantage?
Correct answer: D
Mechanical advantage of a lever = effort arm ÷ load arm = 6 ÷ 1.5 = 4. Dividing the other way (0.25) would mean the lever makes the job harder.
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Question 5
A 60-lb child sits 5 ft from the pivot of a seesaw. How far from the pivot, on the other side, must a 75-lb child sit to balance it?
Correct answer: D
Moments must be equal: 60 × 5 = 75 × d, so d = 300 ÷ 75 = 4 ft. The heavier child must sit closer to the pivot, so any distance of 5 ft or more cannot be right.
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Question 6
What does a single fixed pulley do?
Correct answer: B
A fixed pulley has a mechanical advantage of 1: you pull down with the same force to lift a load up. Only a movable pulley reduces the force.
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Question 7
The 120-lb load hangs from a movable pulley. The rope runs from the ceiling, under the movable pulley, over a fixed pulley and down to the person pulling.
Ignoring friction and the weight of the pulleys, how much force is needed to hold the load?
Correct answer: A
Two rope segments hold up the movable pulley, so each carries half the load: 120 ÷ 2 = 60 lb. The fixed pulley only changes the direction of the pull; it adds no further advantage.
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Question 8
A pulley system has a mechanical advantage of 4. To raise the load 3 ft, how much rope must be pulled?
Correct answer: C
A machine that cuts the force to one-fourth makes you pull four times as far: 3 × 4 = 12 ft. The work (force × distance) stays the same, apart from friction.
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Question 9
Gear A has 12 teeth and drives gear B, which has 36 teeth. Gear A turns at 90 revolutions per minute (rpm).
How fast does gear B turn?
Correct answer: A
Gear B has 3 times as many teeth (36 ÷ 12 = 3), so it turns 3 times slower: 90 ÷ 3 = 30 rpm. 270 rpm comes from multiplying instead of dividing.
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Question 10
Three gears of the same size are in a row. Gear A turns clockwise and drives gear B, which drives gear C.
In which direction does gear C turn?
Correct answer: B
Each pair of meshing gears turns in opposite directions: A clockwise, B counterclockwise, C clockwise again. The middle gear (an idler) only reverses the direction.
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Question 11
When a small gear drives a much larger gear, the larger gear turns
Correct answer: C
The larger gear makes fewer turns, so it is slower, but the force acts on a bigger radius, so the turning force (torque) increases. Speed is traded for torque, as in a low gear on a bicycle.
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Question 12
A belt connects a 4-inch pulley on a motor to a 12-inch pulley on a machine. The motor pulley turns at 600 rpm. How fast does the 12-inch pulley turn?
Correct answer: D
The belt moves the same distance at both rims, so speed × diameter is equal: 600 × 4 = rpm × 12, which gives 200 rpm. The larger pulley turns more slowly.
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Question 13
Two pulleys are connected by a belt that crosses over itself in the shape of an X. If the driving pulley turns clockwise, the driven pulley turns
Correct answer: A
A crossed belt reverses the direction of rotation. An open (uncrossed) belt would turn both pulleys the same way.
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Question 14
A winch has a crank handle with a radius of 15 inches and a drum (axle) with a radius of 3 inches. Ignoring friction, what force on the handle lifts a 250-lb load?
Correct answer: C
The mechanical advantage of a wheel and axle is the radius ratio: 15 ÷ 3 = 5. The force needed is 250 ÷ 5 = 50 lb; 1,250 lb comes from multiplying by 5 instead of dividing.
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Question 15
A single-thread worm drives a worm wheel with 40 teeth. How many turns of the worm are needed to turn the wheel once?
Correct answer: B
Each turn of a single-thread worm moves the wheel by one tooth, so 40 teeth need 40 turns. This is why worm gears give a very large speed reduction.
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