Suppose the traffic investigators determined from the skid marks that these cars came to rest with a displacement of 9.72m at 72 degrees North of East, and the coefficient of friction was .72. The red car had a mass of 1000kg, but the blue car's mass was 1300 kg in this accident. Find the velocities (in mph) of each car immediately before their collision. Solution: I used two formulas that I read in another forum but we have never been taught the first one in class. First I used ( Vf2-Vo2=-2UkgD) then M1V1i+M2V2i=(M1+M2)Vf D=9.72 Theta=72 degrees Uk=.72 M1=1000kg M2=1300kg 1000kg*Vi+1300kg*0=(2300kg)(11.71m/s) =26.93m/s=60.3mph 1000kg*0+1300kg*Vi=(2300kg)(11.71m/s) =20.72m/s=46.4mph I got 60.3 mph for the Red Car and 46.4 mph for the Blue Car. Any idea if that is the correct way to go about this problem.