在光滑水平面上，一物体在水平力F作用下由静止开始运动。若力F增大为原来的2倍，其他条件不变，则物体的加速度变为原来的多少倍？
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Correct answer
C. 2倍
Principle or equation
牛顿第二定律：F = ma。质量不变时，加速度与合外力成正比。
Why this answer is correct
光滑水平面，合外力等于F。a1 = F/m，a2 = 2F/m = 2a1，所以加速度变为原来的2倍。
Example
若F=10 N，m=2 kg，a=5 m/s²；F增大到20 N，a=10 m/s²，为原来的2倍。
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