Solve the below problem:
Q: Determine the moment about the origin O of the force (7.5 N) (3 N) (4.5 F= i+ j - N)k which acts at a point A. Assume that the position vector of A is
(a) r= -(6 m)i+ (3 m)j + (1.5 m)k,
(b) r=(2 m)i-(0.75 m)j-(1 m)k,
(c) r= -(2.5 m)i -(1 m)j+(1.5 m)k.