As maximum static friction = µsN = 0.5 × 10 × g = 50N as 60 N is greater than force of static friciton (maximum) So, block will slip over the lower one and hence force of kinetic friction fk has to be considered in that case and fk = bk N = 0.3 × 10 × 10 = 30 N u = ∞ ⇒ v = f (from formula) Also, h1 = - fθ For plane mirror object distance is d - f.