1. The problem statement, all variables and given/known data You are called as an expert witness to analyze the following auto accident: Car B, of mass 2100 [tex]kg[/tex], was stopped at a red light when it was hit from behind by car A, of mass 1400 [tex]kg[/tex]. The cars locked bumpers during the collision and slid to a stop. Measurements of the skid marks left by the tires showed them to be 7.25 [tex] m [/tex] long, and inspection of the tire tread revealed that the coefficient of kinetic friction between the tires and the road was 0.650. What was the speed ([tex] v [/tex]) of car A ([tex]mph[/tex]) just before the collision? By how many [tex]mph[/tex] was car A exceeding the speed limit 35.0 [tex]mph[/tex]? 2. Relevant equations I have tried 1.) [tex]m_1 v_1i + m_2 v_2i = (m_1+m_2)v_f[/tex] (does not work) 2.) [tex]v_f^2-v_o^2=2-U_k(g)D[/tex] (does not work) 3. The attempt at a solution The first equation above I know will not work because it was designed for a perfect inelastic collision. I need to take into account the friction, that is why I used equation two. [tex]v_f^2-v_o^2=2-U_k(g)D[/tex] [tex]v_f = 0 m/s[/tex] [tex]v_0 = ???[/tex] (need to find for problem #1) [tex]U_k = 0.650[/tex] [tex]g = 9.8 m/s^2[/tex] [tex]D = 7.25m[/tex] Any ideas to what I could be doing wrong?