质量为2 kg的物体置于光滑水平面上，受到两个水平力作用：F1=6 N向东，F2=8 N向北。求物体的加速度大小。
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Correct answer
C. 5 m/s²
Principle or equation
牛顿第二定律 F=ma；力的合成遵循平行四边形定则。
Why this answer is correct
合力大小 F = √(6²+8²) = 10 N；加速度 a = F/m = 10/2 = 5 m/s²。
Example
若F1=3N，F2=4N，质量1kg，则合力5N，加速度5 m/s²。
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