Analysis of an accident scene indicates a car was traveling at a velocity of 69.5 mph (31.1 m/s) along the positive x-axis at the instant the brakes were applied and then traveled a distance of 115 m before hitting an obstacle at a velocity of 5.20 m/s. determine the car's acceleration a (assumed constant) and the time t between applying the brakes and hitting the obstacle. (assume the car is moving in the positive direction. indicate the direction with the sign of your answer.)