Block A, with a Mass of 50 Kg, Rests on a Horizontal

Block A, with a mass of 50 kg, rests on a horizontal table top. The coefficient of static friction is 0.40. A horizontal string is attached to A and passes over a massless, frictionless pulley as shown. The smallest mass m_B of block B, attached to the dangling end, that will start A moving when it is attached to the other end of the string is:

A) 20 kg
B) 30 kg
C) 40 kg
D) 50 kg
E) 70 kg