Glass MCQ with answer and solution

Concept

Glass for panels must not be too thin. Minimum thickness is about 3 mm, which weighs about 7.5 kg/m².

Formula

w = ρ × t = 2500 kg/m³ × 0.003 m = 7.5 kg/m²

Step-by-step solution

1. Density of glass ≈ 2500 kg/m³. 2. Minimum thickness of glass for panels ≈ 3 mm = 0.003 m. 3. Weight per m² = 2500 × 0.003 = 7.5 kg/m². 4. So glass for panels should weigh more than (not less than) 7.5 kg/m².

Explanation

Panel glass must be strong enough, so a minimum thickness of about 3 mm is used. 3 mm glass weighs about 7.5 kg/m². So the weight should be above 7.5 kg/m².

Why the other options are wrong

A: Glass lighter than 7.5 kg/m² is too thin and weak for panels. C: This limit is not a standard value, and it does not set a minimum. D: 10.5 kg/m² (about 4.2 mm) is not the standard minimum limit.

Shortcut

3 mm glass × 2.5 kg/m² per mm = 7.5 kg/m², and this is the minimum.

Common mistake

Choosing '<' instead of '>'. The 7.5 kg/m² value is a minimum, not a maximum.