Calculate the force applied if 100 N/m² pressure is exerted over the area of 0.2m²

The law of the conservation of momentum says that the total momentum of any closed and isolated system cannot

Light from two different sources are incident upon the same side of a polarizing filter. light from one source is polarized with total intensity ip, while light from the other source is unpolarized with total intensity iu. as you rotate the polarizing filter through 360 degrees, the intensity of the transmitted light on the other side varies by a factor of 9. what is the relative intensity of the initial polarized source to the unpolarized source, or ip/iu?

I’ve been stuck on this for a while