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Difficulty: MediumTypes of Stress and Strain

A stationary jib crane consists of a horizontal metal boom attached to a vertical mast. The outer end of the boom is supported by a diagonal steel cable connected higher up on the mast. When a heavy load is suspended from the outer end of the boom, what types of internal stress are primarily experienced by the diagonal cable and the horizontal boom, respectively?

  1. Tension in the cable and compression in the boomAnswer
  2. B
    Compression in the cable and tension in the boom
  3. C
    Tension in the cable and shear in the boom
  4. D
    Shear in the cable and compression in the boom

Answer

Tension in the cable and compression in the boom
The heavy load pulls down on the end of the boom. To support this, the diagonal cable must pull upward and inward toward the mast, which stretches the cable, resulting in tensile stress (tension). The inward horizontal component of the cable's pull pushes the boom horizontally into the mast. This pushing force squeezes the boom, resulting in compressive stress (compression).

Step-by-Step Solution

1
Analyze the forces acting on the diagonal cable.
The downward weight of the load causes the cable to pull back against it to keep the boom from falling.
Identifying the force direction determines the stress. Pulling forces acting along the length of a material create tension.
2
Analyze the forces acting on the horizontal boom.
The diagonal cable pulls inward toward the mast. This inward horizontal force pushes the boom tightly against the mast.
Pushing or crushing forces acting along the axis of a structural member create compression.

Key Concept

Identifying tension and compression in load-bearing structural members.
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Topics

Types of Stress and Strain

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