explain the concept of c.o.m. how ti changes before &and after the motion.How it changes before &after collisions. how it is related to different bodies?

Dear shanky

answer to all these question requires atleast 2 lecture for detail  answer .here i am just giving you the basic concept.

if any system made of diferent body of mass m1,m2,m3...... and at a distance from the reference point from where COM is measered is x1,x2,x3,,,, respectively  .so COM of the system about that point is defibed as

COM = (m₁*x₁+m₂*x₂+m₃*x₃ +......)/(m₁ +m₂ +m₃) =(∑m_ix_i)/∑m_i

now lets consider mass m1 .m2.m3 ..... are moving with velocity V1,V2,V3.....respectively

then the COM is moving =(m₁*v₁+m₂*v₂+m₃*_v3 +......)/(m₁ +m₂ +m₃) =(∑m_iv_i)/∑m_i

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