A book (4 kg) is hanging by a string connected to a rope at point B. One end of the rope is connected to the wall at point A, and the other end is pulled by a person at point C with a tension T. The rope from A to B is 1.5 m long and horizontal, while the rope from B to C makes an angle 30˚ with the horizontal. (See figure, in which we take counterclockwise to be positive.) (Use g = 10 m/s2)
What is the torque due to the weight of the book about point B?