1. The problem statement, all variables and given/known data A small mass m hangs from a thin string and can swing like a pendulum. You attach it above the window of your car. When the car is at rest, the string hands vertically. What angle θ does the string make when the car accelerates at a constant a=1.20m/s^2? 2. Relevant equations I assume a relevant equation is ƩF = ma 3. The attempt at a solution This is already solved in my book but I was trying to do it by myself I know I need to find ƩF = may and ƩF = max And I know that ƩF = may is FTcosθ -mg=may And that ƩF = max is FTsinθ =max My book says that FTcosθ -mg =0, and my question is why???? is ay=0? How can I know that?