Force equilibrium on stationary nail

Steps:

• Nail in equilibrium: forces W, T, R sum to zero vectorially, forming closed triangle.
• W acts vertically downward with magnitude proportional to length.
• T acts upward at 40° to vertical, away from wall, with horizontal component T sin 40° and vertical T cos 40°.
• R acts from wall to balance: horizontal toward wall equaling T sin 40°, vertical downward equaling W - T cos 40° (assuming T cos 40° < W).

Why A is correct:

• Vectors form closed triangle to scale, with T at exact 40° to vertical and R direction/magnitude balancing components per Newton's first law.

Why the others are wrong:

• B: T angle incorrect, not 40° to vertical.
• C: R direction wrong, fails horizontal balance.
• D: Magnitudes disproportionate, triangle doesn't close.

Final answer: A