angle tilted for image

The image formed by a plane mirror is of the same size as the object and is located the same distance behind the mirror as the object in front.

Since the object arrow is inclined at an angle of 30 degrees with the plane of the mirror, the image is also inclined with the same angle (30 degrees) to the mirror, with the foot of the arrow farther away.



2012-07-14 19:15:52 補充：
Your other question:
P is clearly a point of compression. The particle on its left-hand side is displaced to the right, whereas that on the right-hand side is displaced to the left. This makes point P the centre of a compression.

2012-07-16 17:04:28 補充：
Your other question1
I suppose the diagram gives a stationary wave, and the specified time T is in second.
Since after 0.5 s, all points return to the equilibrium position, the period is 4 x 0.5 s = 2 s