A ball of mass 5kg moving with a velocity of 10 collides with a 15kg ball moving with a velocity of 4.if both balls stick together after collision, calculate their common velocity after impact if they initially move in opposite and the same direction

Answer 1

opposite, 5kg ball moving in the + direction:
5(-10) + 15(4) = (5+15)v
v = 1/2

do again, with both moving in the + direction.

Answer 2

rats -- I did it with 5kg moving in the - direction.