A reinforced concrete beam measures 12 in. × 24 in. in cross section. If the density of reinforced concrete is 1 50 lb/ft3, the weight of the beam is
A)350 lb/ft.
B)450 lb/ft.
C)300 lb/ft3.
D)300 lb/ft.
E)300 lb.

Question

Quizplus · Accepted Answer

The weight of the beam per foot can be calculated by first finding the volume of a 1-foot (or 12-inch) section of the beam, then multiplying by the density of reinforced concrete. The volume of a 1-foot section is 12 in. × 24 in. × 12 in. = 3456 in³. Since there are 1728 cubic inches in a cubic foot (12 in. × 12 in. × 12 in.), the volume in cubic feet is 3456 in³ / 1728 in³/ft³ = 2 ft³. Multiplying the volume by the density (2 ft³ × 150 lb/ft³) gives 300 lb/ft.

A Reinforced Concrete Beam Measures 12 In