Question

A 4-meter plank weighing 7kg is lying on a dock with 3.02 meters of its length on the dock, and the rest of its length extending off the dock. If a child weighing 38kg walks out onto the part of the plank extending off the dock, what is the maximum distance in meters that the child can walk on the plank from the edge of the dock before he falls into the water?

Answer 1

Child can walk up to 0.18 m on the plank from the edge of the dock without falling into the water.

The child can only walk on the dock till the moment of the child mass is balanced by the weigh of the plank

Consider the free body diagram

Taking the moment about point O

38×d=7×1.02

d=0.18 m