3. 5 m A D C B 0.5 m 1.3 m Figure 2 A beam ADCB has length 5 m. The beam lies on a horizontal step with the end A on the step and the end B projecting over the edge of the step. The edge of the step is at the point D where DB = 1.3 m, as shown in Figure 2. - la When a small boy of mass 30 kg stands on the beam at C, where CB = 0.5m, the beam is on the point of tilting The boy is modelled as a particle and the beam is modelled as a uniform rod. (a) Find the mass of the beam. (3)