Net force from hanging weight minus friction drives system acceleration Steps:

• Identify hanging mass m₂ = 0.20 kg and surface mass m₁ = 0.50 kg; motion occurs as hanging block descends if m₂g > f.
• Apply Newton's second law to system: m₂g - f = (m₁ + m₂)a.
• Substitute values with g = 9.8 m/s² and a = 2.0 m/s²: 0.20 × 9.8 - f = (0.70) × 2.0.
• Solve: 1.96 - f = 1.40, so f = 1.96 - 1.40 = 0.56 N ≈ 0.5 N.

Why A is correct:

• Matches f = m₂g - (m₁ + m₂)a from Newton's second law for the system, yielding ≈0.5 N.

Why the others are wrong:

• B is tension T ≈ m₂(g + a) = 0.20 × 11.8 ≈ 2.4 N, not friction.
• C approximates m₁g / 10 or similar misapplication, unrelated to net force.
• D is m₁g - m₁a ≈ 0.50 × 7.8 = 3.9 N, confusing surface normal force with friction.

Final answer: A