The length of wire when M1 is hung from it is l1 and is l2 with both M1 and M2 hanging. The natural length of wire is
If two lines have direction cosines
l1,m1,n1 and l2,m2,n2
then the condition for these lines being perpendicular to each other would be -
Let L1 and L2 be two non-vertical lines with slopes m1 and m2 respectively. If α1 and α2 are the inclinations of lines L1 and L2, respectively. the acute angle (say θ) between lines L1 and L2 , is given by