一个质量为1 kg的物体从离地面高5 m处自由下落，不计空气阻力，重力加速度g取10 m/s²。求物体落地时的速度大小。
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Correct answer
B. 10 m/s
Principle or equation
机械能守恒定律：mgh = ½mv²，解得 v = √(2gh)。
Why this answer is correct
v = √(2 × 10 × 5) = √100 = 10 m/s。
Example
若高度为20 m，则v = √(2×10×20)=√400=20 m/s。
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