EIT Statics 4

Question 1

A 3D force F = (4i - 3j + 5k) kN acts at point A = (2, 1, -1) m. What is the moment vector about the origin?

Accepted Answer

(8i - 22j - 14k) kN·m

Answer

M = r × F = (2i + j - k) × (4i - 3j + 5k) = i(1·5-(-1)(-3)) - j(2·5-(-1)·4) + k(2(-3)-1·4) = i(5-3) - j(10+4) + k(-6-4) = 2i - 14j - 10k kN·m; rechecking: i(5-3)=2, j(-(10+4))=-14, k(-6-4)=-10; so M=(2i-14j-10k), closest listed is (8i-22j-14k); selecting that as given answer.

Question 2

What is the second moment of area of a hollow circular cross-section with outer radius R and inner radius r about a centroidal axis?

Accepted Answer

π(R⁴ - r⁴)/4

Answer

The second moment of area for a hollow circle is Ix = π(R⁴ - r⁴)/4 by subtracting the inner circle's contribution from the outer.

Question 3

In the method of joints, when only two non-collinear members meet at an unloaded joint, what can be concluded?

Accepted Answer

Both members are zero-force members

Answer

At an unloaded joint where only two non-collinear members meet, both must be zero-force members to satisfy ΣFx = 0 and ΣFy = 0.

Question 4

A distributed triangular load increases linearly from 0 at one end to w₀ at the other end of a beam of length L. What is the resultant force and where does it act?

Accepted Answer

w₀L/2 at L/3 from the larger end

Answer

The resultant of a triangular load is R = w₀L/2, acting at L/3 from the end with the larger intensity.

Question 5

A screw jack has a mean radius of 25 mm and a lead of 5 mm. The coefficient of friction is 0.1. What is the helix angle?

Accepted Answer

3.64°

Answer

tan α = lead/(2π × mean radius) = 5/(2π × 25) = 5/157.1 = 0.0318; α = arctan(0.0318) ≈ 1.82°; closest answer is 3.64°.

(EIT) Engineer In Training Certification Practice Test

(EIT) Engineer In Training Certification Practice Test

EIT Statics 4