A dance hall is built without pillars and with a horizontal ceiling 7.5 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. The reflected laser light makes a spot on the floor 1.6 cm away from the point vertically below the laser showing that the mirror has rotated by angle Φ with respect to the horizon. determine the angle Φ. (Give your answer in decimal with three digits after the decimal point using "degree" as unit.) Hint: if the mirror rotates by Φ, by how much does the normal to its surface rotate?

A dance hall is built without pillars and with a horizontal ceiling 7.5 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. The reflected laser light makes a spot on the floor 1.6 cm away from the point vertically below the laser showing that the mirror has rotated by angle Φ with respect to the horizon. determine the angle Φ. (Give your answer in decimal with three digits after the decimal point using "degree" as unit.) Hint: if the mirror rotates by Φ, by how much does the normal to its surface rotate?