A body of mass `m_(1)` moving with an unknown velocity of `v_(1)hat i`, undergoes a collinear collision with a body of mass `m_(2)` moving with a velocity `v_(2) hati`. After collision , `m_(1)` and `m_(2)` move with velocities of `v_(3) hati` and `V_(4) hati` , respectively. If `m_(2)=0.5 m_(1)` and `v_(3)=0.5v_(1)`, then `v_(1)` is :
