12. a force f=-k(yi +xj) (where, k is a positive constant) acts on a particle moving in the xy-plane. starting from the origin, the particle is taken along the

12. A force F=-k(yi +xj) (where, k is a positive constant) acts on a particle moving in the xy-plane. Starting from the origin, the particle is taken along the positive X-axis to the point (a,0) and then parallel to the Y-axis to the point (a,a). The total work done by the force F on the particle is (a)-2ka (b) 2ka? (c)-ka (d) ka