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A 3 kg block is pulled with F = 20 N at 30° above horizontal on rough surface (μ_k = 0.4). Find acceleration (g = 10, sin 30° = 0.5, cos 30° = 0.866):
A1.5 m/s²
B2.5 m/s²
C3 m/s²
D5 m/s²
Answer & Solution
Correct answer: C. 3 m/s²
Horizontal component of F: 20 × 0.866 = 17.32 N. Vertical (up): 20 × 0.5 = 10 N. Normal: N = mg - F_y = 30 - 10 = 20 N. Friction = 0.4 × 20 = 8 N. Net horizontal force: 17.32 - 8 = 9.32 N. Acceleration = 9.32/3 ≈ 3.1 m/s² ≈ 3 m/s². Answer: C.
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