what is the effect on coefficient of static friction when side length of acube 5 cm is doubled to original?
The coefficient of friction depends on the materials used, in may depends on temperature, on geometric properties of the interface between the materials. But coefficient of friction is independent of the area of contact. (According to the Amontons' second law of friction, the force of friction is independent of the apparent area of contact).
Hence coefficient of static friction stays the same, when side length of a cube 5 cm is doubled to original.