Answer:
62.5 %
Explanation:
Let the initial intensity of unpolarized light is Io.
After first polariser the intensity of light becomes I'.
So, 
Now it passes through another polariser. The angle between the first polariser and the second polariser is given by Ф. The intensity is I''.
According to the law of Malus

Here, Ф = 30 degree

The percentage change in the intensity is given by

= 62.5 %
The the Water turns to ice. But even then they would never truly stop moving.<span />
Where the force is not perpendicular to the path of motion
are you missing the the situations ?
Answer:
The surface tension of plain water can cause a needle to float.
Evidently, the addition of detergent to the water reduces the surface tension of the liquid causing the needle to sink.