A dance hall is built without pillars and with a horizontal ceiling 7.20 m above the floor. A mirror is fastened flat against one section of the ceiling. Following an earthquake, the mirror is in place and unbroken. An engineer makes a quick check of whether the ceiling is sagging by directing a vertical beam of laser light up at the mirror and observing its reflection on the floor.
(a) Show that if the mirror has rotated to make an angle θ with the horizontal, the normal to the mirror makes an angle θ with the vertical.
(b) Show that the reflected laser light makes an angle 20 with the vertical.
(c) If the reflected laser light makes a spot on the floor 1.40 cm away from the point vertically below the laser, find the angle θ.