Final answer:
The acceleration of the car as it applies its brakes and comes to a stop is -5 m/s², which indicates a deceleration.
Step-by-step explanation:
To determine the acceleration of the car, we use the formula for acceleration: a = Δv/Δt, where Δv is the change in velocity and Δt is the change in time. In this case, the car comes to a stop from an initial velocity of 20 m/s within 4 seconds, meaning Δv = -20 m/s (since the car is coming to a stop) and Δt = 4 s.
The acceleration can be calculated as follows:
a = Δv/Δt = (-20 m/s) ÷ 4 s = -5 m/s².
The negative sign indicates that this is a deceleration because the car is slowing down. When a car applies its brakes, the final velocity is 0 m/s, indicating that it's at rest after coming to a stop.