Bending Moment Calculation:

To calculate the bending moment at a point on the cantilever beam, the following formula can be used:

BM = WL - ∑(wx)

Where, BM = Bending Moment
W = Load (in N)
L = Length of the beam (in m)
x = Distance of the load from the reference point (in m)

Calculation of Bending Moment at Point B and Point C:

Bending moment at point B can be calculated as follows:

BM(B) = 300000 x 0.5 - 500000 x (1.2-0.5) - 800000 x (1.8-1.2)
BM(B) = -400000 Nm

Bending moment at point C can be calculated as follows:

BM(C) = 300000 x 1.2 - 500000 x (1.2-1.2) - 800000 x (1.8-1.2)
BM(C) = 180000 Nm

Comparison of Bending Moment at Point B and Point C:

From the above calculations, it can be observed that the bending moment at point B is -400000 Nm and the bending moment at point C is 180000 Nm. Therefore, the bending moment at point C is lesser than at point B.

Explanation:

The bending moment at a point on the cantilever beam is directly proportional to the load acting on the beam and the distance of the load from the reference point. In this case, the load acting on the beam is maximum at point B (500KN) and the distance of the load from the reference point is also maximum (1.2m). Therefore, the bending moment at point B is maximum. On the other hand, the load acting on the beam is minimum at point C (800N) and the distance of the load from the reference point is also minimum (0.6m). Therefore, the bending moment at point C is minimum. This is the reason why the bending moment at point C is lesser than at point B in this case.