Using knowledge to solve problems (1) The speed of sound propagation in the air at 15℃ is _ _ _ _ _. At the sports meeting, the terminal timekeeper saw the starting gun "smoke".

(1) The speed of sound propagation in air at 15℃ is 34 m/s. When the starter gives the order, light and sound travel forward at the same time, and the speed of light is much faster than the speed of sound. It will take some time for the timing referee to hear the gunshots after seeing the smoke, so the timing error is smaller and more accurate than hearing the gunshots.

(2) "The pool is clear and the water is shallow" means that Looking at the bottom of the water is against the direction of light propagation, that is, against the refracted light. Because of the illusion, we always think that light propagates along a straight line, so the position we see is shallower than the actual position;

The "pool water lighting month" is the image of the moon on the water surface, which belongs to the phenomenon of plane mirror imaging and is formed by the reflection of light.

When the light obliquely enters the water from the air, it is refracted at the water surface, and the angle of refraction is smaller than the incident angle. When the light enters the water, it is close to the normal line and enters the diver's eyes. However, due to the illusion, the diver thinks that the light always travels in a straight line and looks against the direction of the light, forming a virtual image. Therefore, it is higher than the actual position.

(3) First, the normal line is drawn through the incident point, and then the reflected light is drawn on the left side of the normal line with the incident point according to the reflection angle equal to the incident angle, and the degree is equal to the incident angle equal to 9-3 = 6, as shown in the figure:

So the answer is: (1) 34m/s; The propagation speed of light is much faster than that of sound; (2) refraction; Reflection; High; Refraction; (3) See the solution diagram.