The surface mass density (mass per unit area) of a semi-circular disc of radius ‘R’ varies as $\sigma =|\overrightarrow{a}\times \overrightarrow{r}|,$ where $\overrightarrow{a}$ is a constant vector along positive x axis and $\overrightarrow{r}$ is position vector with respect to origin. It is kept on smooth horizontal surface with flat surface in contact with surface. Now, force ‘F’ is applied in such a way that it moves translationally without any rotation. The value of h is $\frac{k\pi R}{16}$ then find value of k.