Question

Which of the following is true for a beam having various forces acting over it?

(a) If we are considering the clockwise direction to be positive then the rotation along the counter clockwise direction is negative

(b) If we are considering the clockwise direction to be negative then the rotation along the counter clockwise direction is also negative as no such assumptions can be taken

(c) If we are considering the clockwise direction to be positive then the rotation along the counter clockwise direction is also positive as no such assumptions can be taken

(d) If we are considering the clockwise direction to be negative then the rotation along the counter clockwise direction is neither positive nor negative as we only pre assumed the clockwise direction

I have been asked this question in homework.

Enquiry is from Shear and Moment Equations and Diagrams in section Internal Forces of Engineering Mechanics

Answer 1

The correct option is (a) If we are considering the clockwise direction to be positive then the rotation along the counter clockwise direction is negative

The explanation: We can take such assumptions. We are free to do so. We just need to specify if clockwise is positive then the counter clockwise is to be negative. Also such assumption are very useful in 2D calculation of the moments caused by various forces on the body.