What kind if force converts potential energy to kinetic energy for magnets and ferromagnetic metals

Find the volume of the ellipsoid x^2+y^2+5z^2=36.

The density of a liquid could be found by using

Light that is polarized along the vertical direction is incident on a sheet of polarizing material. only 96% of the intensity of the light passes through the sheet and strikes a second sheet of polarizing material. no light passes through the second sheet. what angle does the transmission axis of the second sheet make with the vertical?