1. The problem statement, all variables and given/known data A collision occurs between two football players. Player 1 has mass of 75 kg and a velocity of 6 m/s. Player 2 has mass of 150 kg and a velocity of -3 m/s. Assuming an ELASTIC collision, what is the final velocity of player 2? 2. Relevant equations They gave us this equation in class to calculate the final velocity: m = mass Vi = initial velocity Vf = final velocity a = player 1 b = player 2 Vfb = [(2*ma)/(ma+mb)]*Via + [(mb-ma)/(ma+mb)]*Vib 3. The attempt at a solution Using the equation above and plugging in the numbers: Vfb = [(2*75kg)/(75kg + 150kg)]*(6 m/s) + [(150kg - 75kg)/(75kg + 150kg)]*(-3 m/s) which gives me: Vfb = 4 m/s + -1 m/s = 3 m/s The "online" homework solution says it is -3 m/s. Am I incorrect? Did I miss a negative sign somewhere, or is there a principle of momentum that I am not getting?