In a dark laboratory, a small non-reflective box is levitated by a laser with fre- quency ƒ that is aimed vertically upward. The cross-sectional area of the box is half the cross-sectional area of the laser. (a) If the laser emits 20W of power and the box is stationary in the air, what is the mass of the box? (b) How many photons does the laser emit every second? (c) Assuming the light from the laser is originally unpolarized, suppose that a polarizer is placed in the path of the laser. Now replace by non-reflective box by a reflective box. What must the mass of the reflective box be so that it is also stationary in the air?

In a dark laboratory, a small non-reflective box is levitated by a laser with fre- quency ƒ that is aimed vertically upward. The cross-sectional area of the box is half the cross-sectional area of the laser. (a) If the laser emits 20W of power and the box is stationary in the air, what is the mass of the box? (b) How many photons does the laser emit every second? (c) Assuming the light from the laser is originally unpolarized, suppose that a polarizer is placed in the path of the laser. Now replace by non-reflective box by a reflective box. What must the mass of the reflective box be so that it is also stationary in the air?