Final answer:
To calculate the moments ma and mb about point a for the forces applied at points a and b, multiply each force by its distance from the point of rotation. Then, to find the resulting couple moment mr, subtract the moments. Example calculations are provided.
Step-by-step explanation:
The student is asking to calculate moments ma and mb about point a for the forces applied at points a and b and determine the resulting couple moment mr. In order to calculate the moments, we need to know the distances of the forces from point a. The moment is calculated by multiplying the force applied by the distance from the point of rotation:
ma = Fa imes ra
mb = Fb imes rb
To find the resulting couple moment, we subtract the moments:
mr = ma - mb
For example, if Fa is 10 N and ra is 2 m, and Fb is 5 N and rb is 3 m, then the moments would be:
ma = 10 N imes 2 m = 20 Nm
mb = 5 N imes 3 m = 15 Nm
mr = 20 Nm - 15 Nm = 5 Nm