Question

In the calculation of the moment of the force about the axis, the cross product table, i.e. the 3X3 matrix which is made for doing the cross product having 3 rows, contains three elements. Which are they from top to bottom?

(a) Axis coordinates, point coordinates, and the force coordinates

(b) Point coordinates, axis coordinates, and the force coordinates

(c) Axis coordinates, force coordinates, and the point coordinates

(d) Force coordinates, point coordinates, and the axis coordinates

The question was asked in final exam.

Origin of the question is Moment of a Force on a Specified Axis topic in division Force System Resultants of Engineering Mechanics

Answer 1

The correct answer is (a) Axis coordinates, point coordinates, and the force coordinates

To explain I would say: The 3X3 matrix which is being made is having axis coordinates, point coordinates and the force coordinates. They are from top to bottom placed. The order cannot be changed. Or if changed then one needs to apply the negative sign appropriately. Negative because the directions get reversed.