A car driver has rear ended a truck but claims he was driving the speed limit before hitting the brakes. The driver left a 50m long streak of tire rubber when he slammed on the brakes. The mass of the drivers car is 1000kg. The coefficient of friction between the tire and asphalt is 0.5. The mass of the truck that got hit is 5000kg. The speed limit for the road is 40mph. What was the magnitude of the acceleration of the car? (Remember that magnitudes are always positive). How fast was the car going right before the driver slammed on the brakes?