1. The problem statement, all variables and given/known data A.) Find the speed at which Superman (mass=79.0 kg) must fly into a train (mass = 17026 kg) traveling at 70.0 km/hr to stop it. B.) Running into the train at that speed would severely damage both train and passengers. Calculate the minimum time Superman must take to stop the train, if the passengers experience an average horizontal force of 0.500 their own weight. C.) How far does the train then travel while being slowed to a stop? So I put the train traveling to right, positive x-direction and superman traveling left, negative x-direction 2. Relevant equations Pf-Pi = 0 Pf = Pi Ms= 79kg Mt = 17026kg Vti = 70km/hr = 19.444m/s Vft = 0m/s (because it is coming to a stop) Vfs = 0m/s (because it is coming to a stop) Vsi = ? 3. The attempt at a solution Pf = Pi (Ms * Vfs) + (Mt * Vtf) = (Ms * Vsi) + (Mt *Vti) 0 = (Ms * Vsi) + (Mt *Vti) (-Mt * Vti) / Ms = -Vsi (Negative because he is moving to the left I am not getting the right answer, can someone please help me out?