Mechanical Engineering PE Exam Flashcards
6 cards from real NCEES practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Mechanical Engineering PE Exam flashcards as text
On the NCEES PE Mechanical exam, what is 'critical speed' of a rotating shaft?
Answer: The rotational speed at which resonance occurs due to natural frequency matching excitation frequency
Critical speed is the rotational speed at which the shaft's natural frequency coincides with the excitation frequency, causing resonance and potentially catastrophic vibration amplitudes.
In the NCEES PE Mechanical exam, which factor is NOT considered in the modified Goodman fatigue criterion?
Answer: Creep rate at temperature
The Goodman diagram relates mean stress and stress amplitude to ultimate strength and endurance limit; creep rate is a separate high-temperature consideration not included in the Goodman criterion.
For the NCEES PE Mechanical exam, what does 'specific speed' (Ns) characterize in pump selection?
Answer: The shape/type of pump impeller best suited for given flow rate and head conditions
Specific speed is a dimensionless parameter that classifies pump impeller geometry (radial, mixed-flow, axial) based on the design flow rate and head, guiding pump type selection.
On the NCEES PE Mechanical exam, what is 'NPSH available (NPSHa)' in pump system design?
Answer: The absolute pressure head available at the pump inlet above vapor pressure, preventing cavitation
NPSHa is the total absolute head available at the pump suction above the fluid's vapor pressure; it must exceed NPSHr to prevent cavitation.
In the NCEES PE Mechanical exam, what does 'affinity laws' allow engineers to predict for centrifugal pumps?
Answer: Changes in flow, head, and power when pump speed or impeller diameter changes
The pump affinity laws state that flow varies with speed (Q ∝ N), head varies with speed squared (H ∝ N²), and power varies with speed cubed (P ∝ N³) when geometry is held constant.
For the NCEES PE Mechanical exam, which stress state does a thin-walled pressure vessel under internal pressure primarily experience?
Answer: Biaxial tensile stress (hoop and longitudinal)
A thin-walled pressure vessel experiences hoop stress (σh = Pr/t) and longitudinal stress (σL = Pr/2t), both tensile, creating a biaxial stress state.
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