Hi, 1. The problem statement, all variables and given/known data A free falling object of mass "m" falling from some height, collides the floor in speed of 20 m/s (perfectly elastic collision). In his 1/2 height back up he splits into 2 pieces- ¼m which going downward and ¾m keeping upward. The ¼m reaching the floor after ½ second. 1) What is the object velocity right before the split? 2) What is the velocity of the small object (¼m) right after the split? 3) What is the velocity of the big object (¾m) right after the split? 2. Relevant equations 3. The attempt at a solution So I used conservation of energy to solve the first question. the initial height is 20.4m. it means the splitting point happened at 10.2m. mgh = ½mv2 , v= 14.14 m/s Now I'm looking on the second question, because I know the falling time I can use kinematic equation. 0 = 10.2 +v0t +½at2 -10.2 = 0.5v0 + ½⋅(-9.8) ⋅0.52 -7.55 = 0.5v0 v0 = -17.95 To figure out the big object velocity I used the coservation of momentum and here is where I got stuck if a already have a negative velocity which determine the direction should I add a minus sign to the conservation of momentun equation too? -¼mv0 + ¾mV0 = m⋅14.14 here when I put into the equation the negative velocity of v I get V0 = 12.87 in the other hand , with positive momentum : +¼mv0 + ¾mV0 = m⋅14.14 I get V0 = 24.83 For some reason I think the first equation answer is more logical , It doesn't make sense that the ¾m accelarated too much after the split. But it feels wrong when I get negative velocity and in the momentum equation I need to add negative sign as well .The negative velocity will do it anyway, won't it? Thanks a lot!