NCEES Mechanical Engineering 1 — Questions and Answers
Question 1: On the NCEES PE Mechanical exam, the first law of thermodynamics for a closed system states that:
- Entropy always increases
- Heat added equals work done minus change in internal energy
- Change in internal energy equals heat added minus work done by the system (Correct answer)
- Work done equals heat added times efficiency
Correct answer: Change in internal energy equals heat added minus work done by the system
The first law states ΔU = Q – W: the change in internal energy equals heat added to the system minus work done by the system.
Question 2: In NCEES PE Mechanical problems, the Carnot efficiency of a heat engine operating between TH = 600 K and TL = 300 K is:
- 25%
- 33%
- 50% (Correct answer)
- 75%
Correct answer: 50%
Carnot efficiency = 1 − TL/TH = 1 − 300/600 = 0.50 = 50%.
Question 3: Which dimensionless number is used to characterize the ratio of inertial forces to viscous forces in fluid flow, as assessed on the NCEES PE Mechanical exam?
- Prandtl number
- Nusselt number
- Reynolds number (Correct answer)
- Mach number
Correct answer: Reynolds number
The Reynolds number Re = ρVD/μ represents the ratio of inertial to viscous forces and determines laminar vs. turbulent flow.
Question 4: For the NCEES PE Mechanical exam, Bernoulli's equation is valid when flow is:
- Compressible, viscous, and unsteady
- Incompressible, inviscid, and steady along a streamline (Correct answer)
- Turbulent and isothermal
- Through a rotating impeller
Correct answer: Incompressible, inviscid, and steady along a streamline
Bernoulli's equation applies to steady, incompressible, inviscid flow along a streamline.
Question 5: In NCEES Mechanical Engineering fundamentals, the stress-strain curve's elastic region is characterized by:
- Permanent deformation proportional to load
- A linear relationship described by Hooke's Law (σ = Eε) (Correct answer)
- Necking and fracture
- Strain hardening behavior
Correct answer: A linear relationship described by Hooke's Law (σ = Eε)
In the elastic region, stress is proportional to strain via Hooke's Law: σ = Eε, and deformation is fully recoverable.
Question 6: On the NCEES PE Mechanical exam, the heat transfer rate through a flat wall by conduction (Fourier's Law) is:
- Q = hA(T₁ − T₂)
- Q = εσAT⁴
- Q = kA(T₁ − T₂)/L (Correct answer)
- Q = mCpΔT
Correct answer: Q = kA(T₁ − T₂)/L
Fourier's Law of conduction: Q = kA(ΔT)/L, where k is thermal conductivity, A is area, and L is thickness.
NCEES Mechanical Engineering 1
On the NCEES PE Mechanical exam, the first law of thermodynamics for a closed system states that: