Traditional Culture Encyclopedia - Photography major - When someone takes a picture indoors with the window as the background, he just takes a pebble falling from a height outside the window. It is known that the exposure time of this photo is

When someone takes a picture indoors with the window as the background, he just takes a pebble falling from a height outside the window. It is known that the exposure time of this photo is

The actual length of the window frame of 100cm in the photo is 4 cm, so the actual length of the stone movement trace is:

△x = 1.6× 100 4 = 40cm = 0.4m

So the speed of the stone is about v = △×△ t = 0.40.02 = 20m/s.

According to v=gt of free fall, there are

t= v g = 20 10 s=2s

So choose B.