Hi ,

the correct answer is k=2 , and i got it .

work done = F.dx , where dx is the distance b/w final and initial points . let's take two points (0,5/3) and (5/k,0) which lie on the given line

Then , dx = 5/ki + 5/3j

hence , F.dx=0 (bcoz W=0)

i.e. 10/k-5=0

k=2