As shown in the figure below, a screw dislocation with a tangent vector in $+$hat$(k)$ direction and a burgers vector in $+$hat$(k)$ direction of magnitude, $2\mathrm{.}5{10}^{-10}m,$ is located a distance of $r=2nm,$ along the x $-$axis, from a crack tip in copper. Copper has a Young's modulus of $130$ GPa and a shear modulus of $48$ GPa $.$ The crack is loaded in mode III to a stress intensity of $K_{\text{I}\text{I}\text{I}}=0\mathrm{.}1MPa{m}^{\frac{1}{2}}$

Calculate the magnitude and direction of the force per unit length that the crack exerts on the dislocation in units of Pa $.$

$0\mathrm{.}2$:$+x$ direction

$0\mathrm{.}12$:$+x$ direction

$1\mathrm{.}0$:$-$x direction

$0\mathrm{.}8$:$-x$ direction