Physical S3 Light reflection

1. The Laws of Reflection tells that the image formed by a plain mirror is at the same (perpendicualr) distance behind the mirror as the object in front.

The image of the clock is thus at a distance of 5 m behind the mirror.
When the clock slides down along the wall, its image also slides down with the same vertical speed of 0.5 m/s, with the horizontal distance behind the mirror remains unchanged.

2. Since the mirror slides down the wall vertically, there is no change in the horizontal distance between the clock and the mirror, and hence the distance between the image and the mirror. The image remains at the same position on the wall. Hence, the speed of the image is zero.

下次可以試用這個上載圖片的地方：

http://postimage.org/

那就可以直接看圖。

2015-01-17 16:25:56 補充：
這題需要討論一下， Q1 必定是 0.5 m/s，沒有懷疑。

但 Q2。。。。。。

2015-01-17 16:28:06 補充：
不如先這樣想想，如果整幅牆也是鏡，那麼鏡上下移動不會使 image 移動，所以其實答案應否是 0 m/s ???

土扁師兄同意嗎？

https://www.sendspace.com/file/3bgql1

I have attached a diagram for your reference, Tks

Where is the clock and how is it placed ?