A block of mass M = 8 kg is connected to an empty bucket of mass 1 kg by a massless coed running over an ideal pulley. The coefficients of static and kinetic friction between table top and block are 0.5 and 0.4 respectively. Sand is gradually added to the bucket until the block just being to slide. The mass of sand added is : (g = 10 m/s2)
(1) 5 kg
(2) 6 kg
(3) 7 kg
(4) 10 kg