FE Exam common mistakes
FE Exam · Understand the traps and how to avoid them.
Leaves the calculator in degree mode and then differentiates or integrates trigonometric functions, or evaluates inverse trig results, without converting the angle to radians.
Earlier statics or surveying-style problems trained the candidate to work in degrees, and the mode setting is not visible on the display during a fast-paced exam.
What to do instead
Before any calculus, series expansion, or trig identity, switch the calculator to radian mode and write 'rad' next to every angle symbol in the work. If a problem states degrees, convert explicitly (multiply by pi/180) rather than relying on the mode.
Uses a z critical value and divides by n when constructing a confidence interval from a small sample with an unknown population standard deviation.
The normal distribution is over-learned from introductory problems, and the t-distribution is treated as a minor variant rather than a required condition when sigma is unknown and n is small.
What to do instead
Apply a two-question check before every interval: is sigma known, and is n at least 30? If sigma is unknown and n is small, use t with n-1 degrees of freedom and compute s with the n-1 denominator.
Multiplies an annual cost by the number of years instead of using the correct annuity or gradient factor, or applies a per-year factor when the compounding period differs from the payment period.
Cash-flow timing is handled mentally rather than drawn, and nominal annual rates are used directly without converting to an effective rate per payment period.
What to do instead
Draw the cash-flow diagram with arrows at the actual time points before selecting a factor, and convert the nominal rate to an effective rate per payment period (i = (1 + r/m)^m - 1, or r/m for the payment period) before looking up any factor.
Selects the option that documents the issue and waits for a supervisor when the scenario involves an imminent threat to public health or safety, or picks the option that is merely legal rather than the one the engineering canon requires.
Workplace loyalty and legal-permissibility reasoning are over-weighted, and the candidate answers as a private employee rather than applying the profession's public-first duty.
What to do instead
Rank the answer choices against a fixed hierarchy: public health and safety first, then competence and honesty, then client and employer interests. When harm is imminent, choose the option that acts to prevent it, not the one that only reports or records it.
Sums forces or moments without a free-body diagram, omits a reaction moment at a fixed support, or assumes a truss member is zero-force without checking the joint equilibrium.
The candidate tries to save time by shortcutting the diagram, and sign conventions are chosen inconsistently between the horizontal and vertical directions.
What to do instead
Always sketch the free-body diagram with a labeled coordinate system before writing equations, and take moments about the point that passes through the most unknown force lines. Verify each claimed zero-force member by checking that the joint has only two members and no external load or reaction.
Applies Hooke's law or the elastic elongation formula to a stress that exceeds the yield strength, or mixes engineering stress and strain with true stress and strain.
The elastic formulas are the most practiced, and the yield strength check is skipped when the applied load is given directly rather than as a stress.
What to do instead
Compute the applied stress first and compare it to the yield strength before using any elastic relationship. If the stress exceeds yield, state that the deformation is plastic and use true stress/strain or the given hardening model; keep engineering and true quantities consistently labeled.
Combines gage pressure on one side of the energy or hydrostatics equation with absolute pressure on the other, or omits atmospheric pressure when the problem asks for an absolute value.
Problem statements often give gage readings while property tables and the ideal gas law require absolute values, and the reference is not tracked once numbers are substituted.
What to do instead
At the start of the solution, convert every pressure to one reference (usually absolute) and write 'abs' or 'gage' beside each value. Add or subtract atmospheric pressure explicitly in the final step if the requested answer uses a different reference.
Substitutes a Celsius temperature directly into the ideal gas law or an entropy expression, or flips the sign convention for work and heat between the first-law equation and the property tables.
Temperature is read off the problem statement without conversion, and different textbook sign conventions are blended within one solution.
What to do instead
Convert all temperatures to absolute units (kelvin or rankine) immediately after reading the problem, before any substitution. At the top of the work, write the chosen sign convention (for example, work positive out, heat positive in) and check every term against it.
Uses peak voltage or current in a power calculation for an AC circuit, or drops a milli/kilo prefix when substituting into Ohm's law or a reactance formula.
DC formulas are over-practiced and the AC distinction between peak and RMS is glossed over, while unit prefixes are converted mentally under time pressure.
What to do instead
For AC power, use RMS values and state explicitly whether the given value is peak or RMS before squaring. Convert every quantity to base SI units with a written factor (for example, 4.7 kilohms = 4.7 x 10^3 ohms) before substituting.
Selects personal protective equipment, such as a respirator or gloves, as the primary control for a hazard instead of an engineering or substitution control.
PPE is the most familiar control from field experience and is easy to picture, so it is chosen without walking through the control hierarchy.
What to do instead
Before selecting an answer, run the hierarchy of controls in order: elimination, substitution, engineering controls, administrative controls, then PPE. PPE is only correct as the primary answer when higher-level controls are shown to be infeasible in the scenario.