A car accelerates in the +x direction from rest with a constant acceleration of a1 = 1.51 m/s2 for t1 = 20 s. At that point the driver notices a tree limb that has fallen on the road and brakes hard for t2 = 5 s with a constant acceleration of a2 = -5.03 m/s2. Write an expression for the velocity of the car just before it starts braking.