1. The problem statement, all variables and given/known data A 2000-lb car traveling north at 60 mph collides with a 5000-lb car traveling east at 40 mph. The cars stick together after the collision. Find the velocity (magnitude and direction) of the cars just after the collision. 2. Relevant equations conservation of linear momentum 3. The attempt at a solution Firstly, I need to find the masses of each car. Car 1 has weight of 2000 lbs and has a mass of (2000/32.2) about 62 slugs. Car 2 has weight of 5000 lbs and has mass of (5000/32.2) about 155 slugs. That said, the initial momentum of car 1 equals m(1) times v(1) or (62 slugs times 60 mph) = 3720 slug-m/h. Initial momentum of car 2 equals m(2) times v(2) or (155 times 40 mph) = 6200 slug-m/h. So the total initial momentum is 9920 slug-m/h. The final momentum of the cars= (total mass of cars since they stick together) times (new velocity) which equals 217v, so v= 9920/217 or 45.7 mph. To find the direction of velocity after collision, wouldn't I do arctan(40/60) = 33.7 degrees NE. Now I must be doing something wrong because in the back of the book, the answer is 33.3 mph at 31 degrees NE. So i can't figure out what I'm doing wrong.