1. The problem statement, all variables and given/known data A crane is raising a plank carrying two boxes that only differ in weight. The boxes weigh 10kg and 20kg respectively. As the plank tilts toward the heavier box, predict which box will start to slide first. Explain your prediction. 2. Relevant equations Coefficient of static friction = Force of static friction / Normal Force. 3. The attempt at a solution From my attempts at solving with a randomly assigned coefficient of static friction (0.4), it appears as though both boxes begin to move at the same angle, being 21.8. This is simply very counterintuitive to me, and I want to make sure I'm not misunderstanding how the formulae work. Am I right that both boxes begin to move at the same angle?