1. The problem statement, all variables and given/known data Football player 1 with a mass of 110kg is moving at 8.0m/s when he crashed into football player 2 with a mass of 105kg, moving at 12m/s [N]. During the tackle, football player 1 hangs onto football player 2, giving them the same velocity during the 0.3 second collision. A) What is their velocity after the collision? B) What is the net force (affecting each player) during the collision? 2. Relevant equations p = momentum v' = velocity after collision p=mv Δp=mv2-mv1 Net Force = Δp / Δt Conservation of momentum: m1v1 + m2v2 = m(v') 3. The attempt at a solution m1 = 110kg v1 = -8m/s m2 = 105kg v2 = 12m/s Let [N] be positive. A) m1v1 + m2v2 = m(v') 110kg(-8m/s) + 105kg(12m/s) = (110kg+105kg)v' -880kg(m/s) + 1260kg(m/s) = 215kg v' 380kg(m/s) / 215kg = v' v' = 1.76744186 m/s [N] I've verified this answer with the course's book. I'm including it because the answer for part B depends on the answer from part A. B) Net Force = Δp / Δt Net Force = (m1v' - m1v1) / (0.3 seconds) Net Force = [(110kg(1.76744186m/s)) - (110kg)(-8m/s))] / (0.3 seconds) Net Force = [ 194.4186046kg(m/s) + 880kg(m/s) ] / (0.3 seconds) Net Force = (1074.4418605kg(m/s)) / (0.3 seconds) Net Force = 3581.395349kg(m/s2) Net Force on Player 1 = 3581.395 Newtons Net Force on Player 2 (from Newton's 3rd LoM) = -3581.395 Newtons I think this should be correct, but I think I'm doing something wrong. The book's answer work uses the formula : Net Force = (m1v1 - m1v' / (0.3 seconds) for net force, which doesn't make sense to me... seeing as how a change in momentum should be found by subtracting the final value from the initial. By the way, the book's answer for player 1 is : -2280 N .... Which makes sense if you use their formula (the calculations are correct)... but its the formula itself that I don't understand. Any thoughts?