1. The problem statement, all variables and given/known data A 1350kg car travelling at 72km/h collides with a slow-moving car of mass 1650kg, also initially travelling south. After the collision, the velocity of the 2 cars together is 24km/h. Determine the initial velocity at which the second car was travelling. Given: m1=1350kg. vi1 = 72km/h=20m/s vf1 = 24km/h=6.6666666m/s m2=1650kg vf2=6.6666666m/s 2. Relevant equations m1vi1+m2vi2=m1vf1+m2vf2 3. The attempt at a solution 1350(20)+1650(x)=1350(6.66666666)+1650(6.66666666) 27000+1650x=9000+11000 27000+1650x=20000 1650x=-7000 x=-4.24242424m/s=-15.2727272km/h My answer was right except for the negative sign. Does the negative sign mean I did something wrong, because I didn't put negative signs infront of the velocity values in my calculations to indicate direction. What did I do wrong?