Halliday, Resnick & Walker — Center of Mass and Linear Momentum: Problem 56

56 In the "before" part of Fig. 9-52, car A (mass 1100 kg) is stopped at a traffic light when it is rear-ended by car B (mass 1400 kg). Both cars then slide with locked wheels until the frictional force from the slick road (with a low \(\mu_k\) of 0.10) stops them, at distances \(d_A = 8.2 \text{ m}\) and \(d_B = 6.1 \text{ m}\). What are the speeds of (a) car A and (b) car B at the start of the sliding, just after the collision? (c) Assuming that linear momentum is conserved during the collision, find the speed of car B just before the collision. (d) Explain why this assumption may be invalid.