7.
(2023高一上·郑州期末)
利用超声波遇到物体发生反射,可测定物体运动的有关参量。如图所示仪器A和B通过电缆线连接,B为超声波发射与接收一体化装置,仪器A对B提供超声波信号而且能将B接收到的超声波信号进行处理并在屏幕上显示出波形。现固定装置B,并让它对准匀速行驶的小车C,使其每隔固定时间
![](//math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3ET%3C%2Fmi%3E%3Cmn%3E0%3C%2Fmn%3E%3C%2Fmsub%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E0.8%3C%2Fmn%3E%3Cmtext%3Es%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
发射一短促的超声波脉冲(如图2中幅度大的波形),而B接收到由小车C反射回的超声波由A处理后显示成图2中幅度较小的波形,反射滞后的时间在图2已标出,其中,
![](//math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3ET%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E0.2%3C%2Fmn%3E%3Cmtext%3Es%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,
![](//math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3E%CE%94%3C%2Fmi%3E%3Cmi%3ET%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E0.%3C%2Fmn%3E%3Cmtext%3E1s%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
, 超声波在空气中的速度为340m/s。由所给信息可知小车速度为( )
![](//tikupic.21cnjy.com/2023/02/06/6b/d2/6bd2812b2d09cbf7c64346331e2ed864_664x216.png)