A particle of mass ‘m’ moving with a velocity 3i∧+2j∧  m/s,  collides with a stationary mass ‘M’ and finally m moves with velocity −2i∧+j∧m/s.   If  mM =  113,  the velocity of the M after collision is,

Applying law of conservation of  linear momentum let final velocity of M be V m(3i∧+2j∧)+0  =  m(−2i∧+j∧)+M⋅V  ⇒    m(3i∧+2j∧+2i∧−j∧)   =M⋅V;    V   =   mM (5i∧+j∧)     ∴      V   =   113 (5i∧+j∧)m/s ⇒V=(5i∧13+j∧13)  ms-1=final velocity of M