38. 如下圖所示,欲使50 kgf之物體不沿斜面上下滑動,試問W之範圍為何? (斜面摩擦係數 μ = 0.4 )(A) 13 kgf ≤ W ≤ 45 kgf(B) 14 kgf ≤ W ≤ 46 kgf(C) 15 kgf ≤ W ≤ 47 kgf(D) 16 kgf ≤ W ≤ 48 kgf