CAR P BARBARA ALEX Suppose that Alex is parked by the side of a highway, watching car P speed past. Barbara is driving along the highway at constant speed and is also watching car P, suppose that Barbara's velocity relative to Alex is a constant 52 km/h and car P is moving in the negative direction of the x-axis. (a) If Alex measures a constant -78 km/h for car P, what velocity will Barbara measure? (b) If car P brakes to a stop relative to Alex (and thus relative to the ground) in time t = 10 s= at constant acceleration, what is its acceleration relative to Alex? NOTE: 1 1 sec = hour 3600 (c) What is the acceleration of car P relative to Barbara during the braking?