Answer to Question #271323 in Physics for kay

Question

A uniform plank AB, of weight W, is 10 m long. A force of 30 N is applied at end A and the plank is balanced on a pivot placed 2 m from end A. Given that the plank is in equilibrium, calculate the weight of the plank. 

Answer 1

The torque the plank creates and the torque of the force:

$$2·30+\frac22·\frac 2{10}W=\frac82·\frac8{10}W,\\\space\\ W=20\text{ N}.$$