74. A bead of mass m is fitted on to a rodwith a length of 2l, and can move n it with friction having the coeff of frictionμ. at the initial moment the bead is in the middle of the rod. the rod moves translatory in a horizontal plane with an acceleration a in the direction forming an angle alpha with the rod find the time when the bead will leave the rod. (neglect the weight of the bead)