NCEES Statics 3 — Questions and Answers
Question 1: A 600 N box rests on a surface with a coefficient of static friction μs = 0.35. What is the maximum friction force before sliding begins?
- 171 N
- 210 N (Correct answer)
- 245 N
- 300 N
Correct answer: 210 N
F_max = μs × N = 0.35 × 600 = 210 N.
Question 2: At an unloaded joint where only two non-collinear members meet, those members carry:
- Equal tension forces
- Equal compression forces
- Zero force (Correct answer)
- Forces determined by the joint geometry
Correct answer: Zero force
By equilibrium at an unloaded joint with two non-collinear members, both must be zero-force members.
Question 3: The centroid of a triangle is located at what fraction of the height measured from the base?
- 1/4
- 1/3 (Correct answer)
- 1/2
- 2/3
Correct answer: 1/3
The centroid of a triangle is located at h/3 from the base, or one-third of the total height.
Question 4: A force F = 50 N acts at an angle of 30° above the horizontal. What is the horizontal component Fx?
- 25.0 N
- 37.5 N
- 43.3 N (Correct answer)
- 50.0 N
Correct answer: 43.3 N
Fx = F cos(30°) = 50 × 0.866 = 43.3 N.
Question 5: Varignon's theorem states that the moment of a resultant force about a point equals:
- The product of the resultant and the longest moment arm
- The sum of the moments of its components about that point (Correct answer)
- The cross product of the resultant and a unit vector
- Half the area of the force-couple system
Correct answer: The sum of the moments of its components about that point
Varignon's theorem states M_R = ΣM_components, allowing force components to replace the resultant.
Question 6: A concurrent force system has F1 = 10i + 5j kN and F2 = −4i + 8j kN. What is the resultant?
- 6i + 3j kN
- 6i + 13j kN (Correct answer)
- 14i + 13j kN
- −6i + 13j kN
Correct answer: 6i + 13j kN
R = (10−4)i + (5+8)j = 6i + 13j kN by vector addition.
Question 7: What is the moment of inertia of a rectangle (width b, height h) about its centroidal axis parallel to b?
- bh²/6
- bh³/12 (Correct answer)
- b²h/12
- bh³/3
Correct answer: bh³/12
The centroidal moment of inertia of a rectangle about its horizontal axis is I = bh³/12.
NCEES Statics 3
A 600 N box rests on a surface with a coefficient of static friction μs = 0.35.
What is the maximum friction force before sliding begins?