If one ball with a momentum of 50 kg m/s hits a ball at rest an no other forces are acting on either ball ,what's the total momentum of both balls after the collision ?

The total momentum of both ball=Momentum of moving ball+momentum of ball at rest
Because the ball is at rest, there would be no velocity and if no velocity than momentum of object at rest will be=0
therefore total momentum  =50+0
                                           =50 Kg m/s

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