Physics eighth grade, eighth grade, second grade, stroboscopic photography, echo soundtrack

The sound travels back and forth twice (19 meters), and the time is =19 * 2/340 = 0.117 seconds, so it can be heard.

The second question is that you should have missed the picture. I checked. The answer is as follows.

① According to figure 1, a moves in a straight line at a uniform speed.

Do variable speed linear motion.

(2) Write your judgment method:

Compare whether the distances traveled in the same time are equal.

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