Question

Which of the following is correct in bending moment diagram w.r.t the moment (M) of the force (F) acting on the body at a distance L from the axis of the rotation?

(a) M=FLsinθ

(b) M=FLcosθ

(c) M=F.Lsinθ

(d) M=FxLsinθ

This question was addressed to me in examination.

This question is from Bending Moment Diagram topic in chapter Internal Forces of Engineering Mechanics

Answer 1

Correct answer is (a) M=FLsinθ

To explain: The moment of the force about the axis of rotation by the application of the force on the body is given by the cross product of both. If the force not perpendicular to the axis, and making angle θ then cosine form of angle is used. As usually used in the cross product.