A disk of mass M and radius R rolls without slipping down a plane inclined from the

Question:

A disk of mass M and radius R rolls without slipping down a plane inclined from the horizontal by an angle a. The disk has short weightless axle of negligible radius. From this axis is suspended a simple pendulum of length l < R and whose bob has a mass m. Consider that the motion of the pendulum takes place in the plane of the disk, and find Lagrange’s equations for the system.