An equilateral triangle with uniform density is placed on a board with an extremely
large coefficient of friction. One end of the board is raised up slowly. At what angle of
inclination θ does the triangle tip over?

Question

An equilateral triangle with uniform density is placed on a board with an extremely
large coefficient of friction. One end of the board is raised up slowly. At what angle of
inclination θ does the triangle tip over?

festinger · Answer

What this question asks is that at what point does the moment by the weight of the triangle change from clockwise to anti-clockwise?|dw:1478239225778:dw|
"extermely large coefficient of friction" means that this triangle piece does not slip when it is lifted.