1. The problem statement, all variables and given/known data A simple pendulum of length ξ and mass m is suspended from a point on the circumference of a thin massless disc of radius α that rotates with a constant angular velocity ω about its central axis as shown in Figure. Find the equation of motion of the mass m. 2. Relevant equations L = T - V 3. The attempt at a solution Firstly, I know I should find its x' and y' which representing its velocity. i.e. T - V = 1/2 m ( x_dot 2 + y_dot 2 ) - mgy However, I don't know where I should start with to find their x and y. Thanks.