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问题 选择题

图甲为一列简谐横波在某一时刻的波形图,图乙为质点P以该时刻为计时起点的振动图象,下列说法正确的是（   ）

A．从该时刻起经过0.25s时,质点P到达波峰

B．从该时刻起经过0.25s时,质点Q的加速度大于质点P的加速度

C．从该时刻起经过0.40s时,质点Q运动的路程大于质点P运动的路程

D．从该时刻起经过0.15s时,波沿x轴的正方向传播了3 m

答案

答案：D

题目分析：通过乙图可得波的传播周期为 ，P点在此时刻后将向下振动，所以P点在0.35s时到达波峰，A错误；此时P向下运动，Q点向上运动．经过时，P点到达波谷，Q点到达平衡位置上方，但未到波峰，质点Q的加速度小于质点P的加速度．故B错误．根据走坡法可得波向x负方向传播，所以P振动的比Q的步调快，故从该时刻起经过0.40s时,质点Q运动的路程小于质点P运动的路程，C错误；因波沿x轴的正方向传播，λ=4m，则波速，则经过0.15s，波传播距离x=vt=3m．故D正确．

故选D

点评：波的图象往往先判断质点的振动方向和波的传播方向间的关系．同时，熟练要分析波动形成的过程，分析物理量的变化情况．

多项选择题

建筑钢材中可直接用作预应力钢筋的有( )。

A．冷拔低碳钢丝

B．冷拉钢筋

C．热轧Ⅰ级钢筋

D．高强度钢丝

E．钢绞线
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