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Fluids practice questions

22 questions from the mechanical aptitude practice test.

Fluids practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Why is oil rather than air used to transmit force in a hydraulic jack?

  1. Oil is lighter than air
  2. Oil is nearly incompressible
  3. Oil cannot ever leak out
  4. Oil expands under load
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B. Oil is nearly incompressible

A liquid hardly changes volume under pressure, so movement at the pump piston is passed directly to the ram. Air would squeeze down like a spring before the load moved.

Reference: Hydraulics: incompressibility of liquids

A car's brake pedal feels soft and spongy and sinks farther than normal. What is the most likely hydraulic cause?

  1. Too much fluid in the reservoir
  2. Brake fluid that is too thick
  3. Brake lines that are too short
  4. Air trapped in the brake lines
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D. Air trapped in the brake lines

Air is compressible, so part of the pedal travel goes into squeezing the bubbles instead of moving the wheel pistons. Extra fluid in the reservoir does not make the system compressible.

Reference: Hydraulics: incompressibility of liquids

A narrow standpipe and a wide tank are both filled with water to a depth of 20 ft. How do the pressures at their bottoms compare?

  1. They are equal
  2. The wide tank is higher
  3. The narrow pipe is higher
  4. It depends on the volume
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A. They are equal

Liquid pressure depends on depth and the liquid's density, not on the shape or volume of the container. The wide tank holds more weight, but it is spread over a proportionally larger area.

Reference: Fluid pressure depends on depth, not container shape

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