1. The problem statement, all variables and given/known data A 750 kg car is traveling north at 54 km/h while a 1200 kg truck travels south at 83 km/h. The two vehicles are about to have a head-on collision. 1.1) Convert the speed's of both car's into m/s. 1.2) After impact, the car rebounds backwards with a velocity of 18 km/h. Calculate the velocity of the truck after the collision. 2. Relevant equations Pbefore = Pafter P = impulse MaUa + MbUB = MaVa + MbVb U = initial velocity V = final velocity M = mass in kilograms 3. The attempt at a solution 1.1) km/h to m/s (kilometers per hour to metres per second): You divide the value in km/h by 3.6 Therefore the speed of the car in m/s: 54 / 3.6 = 15 m/s And the speed of the truck in m/s: 83 / 3.6 = 23.06 m/s 1.2) So if we take north to be positive then the car is moving in the positive direction and the truck is approaching in a negative direction. So Ua = +15 m/s Ub = -23.06 m/s And if car A rebounds in the opposite direction than Va is -5 m/s (18/3.6 = 5) and Vb will be +. So if I then plug in all my values into the formula: Pbefore = Pafter MaUa + MbUB = MaVa + MbVb 750 * 15 + 1200 * -23,06 = 750 * -5 + 1200 * Vb Therefore Vb = -10,56 or 10,56 in the original direction of the car (north and we took north to be positive) (+10,56 m/s) The answer in the memo is 35,56 m/s They say that both Ua and Ub are positive so Ua = 15 and Ub = 23,06 which conceptually does not make sense as they are heading towards each other from opposite directions and velocity is a vector so it has both magnitude and direction. Is my answer correct or am I making a mistake in my logic or calculations? Any help is appreciated, Thanks!