The acceleration of the car with two washers added to the string would be

Answer 1

greater than the acceleration of the car with only one washer added to the string.

This is because adding more washers increases the total mass attached to the string, which in turn requires more force to accelerate. So, the car with two washers added to the string would experience a greater resistance to acceleration compared to the car with only one washer added, resulting in a slower acceleration.