(a) This car is speeding up as it moves toward the right (positive x-direction), so it has positive acceleration in our coordinate system. (b) This car is slowing down as it moves toward the right, so...(a) This car is speeding up as it moves toward the right (positive x-direction), so it has positive acceleration in our coordinate system. (b) This car is slowing down as it moves toward the right, so it has negative acceleration in our coordinate system because the acceleration is toward the left (negative x-direction).