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GAN aptitude test

Mechanical comprehension test: one rule at a time

By the nodiexam team Updated

Mechanical comprehension questions show a simple machine and ask what it does: which way a gear turns, how hard you must pull, which point holds the most pressure. A few rules answer most of them. Mechanical Reasoning shows a picture of a simple, everyday mechanism and asks a question about it, with no special knowledge needed.

Mechanical questions show a picture and ask about it. You do not need to know how to build anything. You need the rule that each simple machine follows, and the habit of checking the picture against it. One union program even names the section after a classic mechanical test: Pipe Fitters Local 597 in Chicago lists five sections, numerical reasoning, numerical comprehension, spatial reasoning, reading and Bennett mechanical aptitude.

Gears

  • Direction. Two meshed gears turn opposite ways. Count the meshes from the driver: an even count means the same way as the driver, an odd count means the opposite way. Gears fixed on one shaft turn together, the same way.
  • Speed. A gear with fewer teeth turns faster. Driver speed times driver teeth equals driven speed times driven teeth. Gears in the middle of a row (idlers) change the direction but not the speed of the last gear.
Six meshed gearsSix gears, each marked with a letter. Gear A is the driver and turns counterclockwise. Gear A meshes with gear C. Gear C meshes with gear E. Gear E meshes with gear F. Gear E meshes with gear D. Gear A meshes with gear B.ACEFDB

Worked example. Gear A turns counterclockwise, as the arrow shows. Which other gear turns the same way as gear A?

  1. Gear A meshes with gears B and C, so both turn clockwise.
  2. Gear C meshes with gear E, so gear E turns counterclockwise, the same way as gear A.
  3. Gear E meshes with gears D and F, so those two turn clockwise again.

The answer is gear E, two meshes away from gear A.

Gear train with tooth counts3 gears in a row, each marked with a letter and its number of teeth. Gear A, 36 teeth, is the driver and turns counterclockwise. Gear A meshes with gear B, 24 teeth. Gear B meshes with gear C, 18 teeth.ABC36 teeth24 teeth18 teeth

Worked example. Gear A, with 36 teeth, turns at 180 rpm. Gear B, with 24 teeth, sits between it and gear C, with 18 teeth. How fast does gear C turn?

  1. Gear B is an idler. It passes the motion on and does not change the last gear's speed.
  2. Use the first and last gears only: 180 × 36 ÷ 18 = 360.

Gear C turns at 360 rpm. It has half as many teeth as gear A, so it turns twice as fast.

Belts

  • An open belt keeps the direction. A crossed belt, drawn as an X, reverses it.
  • Speed works like gears, with diameters instead of teeth: the smaller pulley turns faster.
Pulleys joined by beltsBelt drive with 2 pulleys, each marked with a letter and its diameter. Pulley A, 9 inches across, is the driver and turns clockwise. An open belt joins pulley A to pulley B, 18 inches across.AB9 in.18 in.

Worked example. Pulley A, 9 inches across, turns clockwise at 50 rpm. An open belt joins it to pulley B, 18 inches across. Which way and how fast does pulley B turn?

  1. An open belt keeps the direction: clockwise.
  2. Speed: 50 × 9 ÷ 18 = 25.

Pulley B turns clockwise at 25 rpm. The bigger pulley turns slower.

Levers

  • A lever balances when weight times distance from the pivot (the fulcrum) is the same on both sides.
  • To lift a load with less force, push farther from the fulcrum.
Beam balanced on a fulcrumA beam rests on a fulcrum. Distances are measured from the fulcrum. A weight of 240 lb sits 9 feet left of the fulcrum. A weight marked ? sits 5 feet right of the fulcrum.?240 lb5 ft9 ft

Worked example. A 240 lb weight sits 9 feet left of the fulcrum. What weight 5 feet to the right balances the beam?

  1. Left side: 240 × 9 = 2,160.
  2. The right side needs the same: 2,160 ÷ 5 = 432.

The answer is 432 lb. The nearer weight must be the heavier one.

Pulleys

  • A single fixed pulley only changes the direction of the pull.
  • With a moving pulley, count the rope strands that hold up the moving block. The pull needed is the load divided by that count, and you pull that many feet of rope for each foot the load rises.
Pulleys lifting a loadPulley system. The rope is tied to the ceiling. It runs down and under pulley 1, on the moving block; up and over pulley 2, fixed to the ceiling; down and under pulley 3, on the moving block; up and over pulley 4, fixed to the ceiling; then down to the hand, which pulls down with 85 lb. The load, marked ?, hangs from the moving block.?85 lb

Worked example. You pull down on the rope with 85 lb. How heavy a load can the pulleys hold still?

  1. Count the strands that hold up the moving block, the one the load hangs from: 4.
  2. Each strand carries the pull: 85 × 4 = 340.

The answer is 340 lb. The rope you hold does not count when it runs down from a fixed pulley.

Ramps and wheels

  • With no friction, push times the length of the ramp equals the load times the height. A longer ramp to the same height needs less push.
  • A wheel and axle works like a lever: the force on the wheel's rim times the wheel's radius equals the load times the axle's radius.
Ramp with a boxA ramp shaped like a right triangle. Length along the slope: 15 ft. Height: 6 ft. A box weighing 690 lb sits on the slope. An arrow shows a push along the slope, marked with a question mark.690 lb?15 ft6 ft

Worked example. With no friction, what push along the slope moves a 690 lb box up a ramp 15 feet long and 6 feet high?

  1. Push × length = load × height, so push × 15 = 690 × 6 = 4,140.
  2. Push = 4,140 ÷ 15 = 276.

The answer is 276 lb. A ramp trades a longer path for a smaller push.

Fluids and springs

  • Pressure and depth. Pressure in a liquid grows with depth. Two points at the same depth have the same pressure, whatever the shape of the tank.
  • Pipes. The same flow goes faster through a narrower pipe. Half the diameter means a quarter of the area, so four times the speed.
  • Hydraulics. A small piston pushing on a large one multiplies the force by the ratio of their areas, and the large piston moves a shorter distance by the same ratio.
  • Springs. Two springs one below the other stretch twice as far under the same weight. Side by side, they share the weight and stretch half as far.
Tank of water with pointsAn open tank of water 8 ft deep, drawn to scale. Point A is 3 ft below the water surface. Point B is 1 ft below the water surface. Point C is 6 ft below the water surface.ABC

Worked example. Which point has the least water pressure?

  1. Pressure depends only on how deep a point sits below the water line.
  2. Point B is the shallowest, at 1 foot. Points A and C sit deeper, at 3 and 6 feet.

The answer is point B.

Hydraulic pressTwo cylinders full of oil, joined by a pipe at the bottom, each with a piston. Small piston area: 3 square inches. Large piston area: 15 square inches. The small piston is pushed down with 225 lb. The force of the large piston is marked with a question mark.oil225 lb?3 sq in15 sq in

Worked example. A 225 lb push on a 3 square inch piston drives a 15 square inch piston. How hard does the large piston push?

  1. The large piston has 15 ÷ 3 = 5 times the area.
  2. So it pushes 5 times as hard: 225 × 5 = 1,125.

The answer is 1,125 lb. It moves only one fifth as far as the small piston.

Spring setupsIdentical springs hang from one ceiling, drawn before they stretch. Setup A: two springs side by side joined by a bar, holding a 48 lb box. Setup B: one spring, holding a 48 lb box. Setup C: two springs in a chain, one below the other, holding a 48 lb box.48 lb48 lb48 lbSetup ASetup BSetup C

Worked example. All the springs are the same. Which box moves down the farthest?

  1. Setup A: two springs side by side share the 48 lb, 24 lb each.
  2. Setup B: one spring holds all 48 lb.
  3. Setup C: two springs in a chain each hold all 48 lb, so the box drops twice as far as in setup B.

The answer is setup C.

Keep practicing

The free GAN practice test has a full mechanical section with a drawing for every question. The GAN study guide covers the other sections, the paper folding guide the spatial part, and the GAN aptitude test overview how programs score the test.

Questions people ask

What is on a mechanical comprehension test?

Pictures of simple machines with a question about each: gears, belts, levers, pulleys, ramps, springs, pistons and tanks. You need a few rules, not physics formulas you have to memorize. The rules on this page cover most question types.

How many mechanical questions are on the GAN test?

GAN does not publish how many questions each section has or how long each section lasts. one applicant at Pipe Fitters Local 597 wrote that the mechanical part was larger than GAN's guide suggests, about 40 to 50 questions. Our practice test gives the section 45 questions in 30 minutes, which is our own choice.

How do I get faster at mechanical reasoning?

Learn the rule for each kind of machine, then drill one kind at a time until you can answer without working it out. Gear direction and belt questions should take seconds. Save your time for the lever and pulley questions that need a short sum.

Sources

Facts on this page come from these pages. We checked each one on the date shown.