Hi,

 

I had done this qn. some days ago. What Govindsuku thought first was right. The answer is (b). I will explain :

 

Consider the rod touching the wall at 'x' distance from the ground and the ground at 'y' distance from the wall. So : x² + y² = l²

 

Differentiating with respect to time, t : x² / t + y² / t = l² / t

 

                                                     : 2xx / t + 2yy / t = 0

 

                                                     : 2xv_x = - 2yv_y

 

ie, When y decreases; x increases; v_x decreases. 

 

What do you say ??!!