QUESTION $2[25$ Marks$]$

a$)$ Define the following terms

i$.$ Rigid body

ii$.$ Newton Second Law

iii. A Couple

iv$.$ A position Vector

$[10$ marks$]$

b$)$ Fig. $3$ shows three forces $F_1=\{100i-120j+75k\}lb,F_2=\{-200i+250j+100k\}lb$ and $F_3=\{-120i+180j+60k\}lb$ acting as shown, determine the resultant moment produced by these forces about point $O$ expressing the result as a Cartesian vector.

$[15$ marks$]$

Fig. $3$