Final answer:
The acceleration of the car, when a braking force of 400N is applied to its 100kg mass, is calculated as 4 m/s² in the negative direction.
Step-by-step explanation:
To find the acceleration of the car, we can use Newton's second law of motion, which states that the net force acting on an object is equal to the product of its mass and acceleration. In this case, the net force is the force exerted by the brakes, which is 400N, and the mass of the car is 100kg. Rearranging the formula, we have:
Force = mass x acceleration
Substituting the given values, we get:
400N = 100kg x acceleration
Solving for acceleration, we divide both sides of the equation by 100kg:
acceleration = 400N / 100kg
acceleration = 4 m/s²
Therefore, the acceleration of the car is 4 m/s².