This problem is an equation derivation question. An equation needs to be derived. This equation is then used to make a procedure to find the required variables (You are an engineer onsite). 1. The problem statement, all variables and given/known data Two cars collide on a road and leave skid marks on the road. They 'hook bumpers' and move as one. Derive and equation to calculate their initial velocities to find the speeding car. 2. Relevant equations m1v1 + m2v2 = m1v1' + m2v2 ' 3. The attempt at a solution Key Assumptions: 1. The net force on the cars is zero. m1v1 + m2v2 = m1'v1' + m2'v2 ' Since the cars move as one, we can put the speeds of both cars together: m1v1 + m2v2 = (m1 + m2)(v') Now I am not sure where to go from here because of many missing variables. The mass of the cars can be found by weighing them. Not sure about the final velocity, you just have skid marks on the road. Any help would be appreciated. Thanks!