Question $2(20$ marks$)$

A simply supported beam $AB$ has a span of $20m.$ A train of loads shown in Figure $2$ below crosses the beam.

a$)$ Determine the position $($indicate clearly in a diagram$)$ and magnitude of the absolute maximum bending moment on the beam due to these loads.

b$)$ Determine the maximum values of positive and negative shear force at any point on the beam. $(10)$

Figure $2$: Train of loads