Sudden planar describes which observation?

• A. Sudden crack in column and noticeable collapse
• B. Thin planar crack crosses column and block slides easily
• C. Nonplanar fracture of noticeable thickness followed by compression of layer with noticeable taps
• D. Planar shear that required at least one tap to cross column and block doesn't slide easily

Answer: (B)

The key idea is a flat, single-plane fracture that appears suddenly and allows the block to move with little resistance. When you see a thin, planar crack crossing a column, it creates a clear surface of weakness. If the block then slides easily along that plane, it matches the sudden planar observation exactly: a thin, flat fracture that enables easy movement.

Other descriptions describe different fracture behavior. A sudden crack with collapse suggests a more catastrophic failure, not just a planar surface that enables easy sliding. A nonplanar fracture with noticeable thickness and subsequent taps implies a rough, irregular break rather than a smooth plane. A planar shear that requires a tap to cross the column indicates friction along a plane rather than an immediately sliding surface.