Vector Sum to Zero for Equilibrium

Steps:

• Identify forces: weight (mg downward), normal (perpendicular to slope), friction (parallel up slope).
• For equilibrium, forces sum to zero, forming closed vector triangle.
• Draw weight vertical; normal at angle θ to vertical (θ = slope angle); friction horizontal component balances.
• Match triangle where vectors head-to-tail close, with directions matching force orientations.

Why C is correct:

• Newton's first law requires vector sum of forces = 0; C shows closed triangle with weight vertical, normal perpendicular to slope, friction parallel, satisfying equilibrium.

Why the others are wrong:

• A: Friction direction reversed, preventing closure.
• B: Normal not perpendicular to slope, violating surface constraint.
• D: Weight not vertical, ignoring gravity direction.

Final answer: C