ASVAB · Structural Support

A beam is supported at both ends and a 200-lb weight is placed exactly in the middle. How much weight does each support hold?

Correct answer

100 lbs each

  1. A 200 lbs each
  2. B 100 lbs each
  3. C 50 lbs each
  4. D 400 lbs each

Why this is the answer

For a symmetric load on a symmetrically supported beam, each support carries half the load. 200 lbs / 2 = 100 lbs at each support. (Note: this assumes the beam's own weight is negligible; if the beam itself weighs 50 lbs, then each support holds 100 + 25 = 125 lbs.) For ASYMMETRIC loads, use the lever/torque principle: torque around one support = torque around the other. If a 200-lb weight is placed 1/4 of the way from support A to support B: support A holds 3/4 × 200 = 150 lbs (because A is farther from the weight in terms of which side bears more — actually closer to the weight bears more). Wait, the rule: the support CLOSER to the load bears MORE. If load is 1/4 from A: distance from A = 1/4 of beam length, distance from B = 3/4. Force at B × 3/4 = Force at A × 1/4. With total weight 200 lbs: F_A = 200 × (3/4) = 150 lbs (at the closer support A), F_B = 200 × (1/4) = 50 lbs (at the farther support B). Verify: F_A + F_B = 200 ✓; torques balance ✓. Beam questions on ASVAB MC: (1) Identify which support bears more weight (the one closer to the load); (2) Calculate the load on each support; (3) Handle cantilever beams (only one support); (4) Add the beam's own weight when given. Cantilever beams: full load and reaction force at the single support; bending moment increases with distance from support. Structural support principles: triangular shapes are strongest; arches transfer load to abutments; suspension cables work in tension; columns work in compression.
Source: ASVAB MC, Beam Loading