Final answer:
The deceleration of the car is 11.11 m/s². This is calculated by dividing the change in velocity, which is -20 m/s (since the car comes to rest from 20 m/s), by the time taken to stop, which is 1.8 s.
Step-by-step explanation:
To calculate the deceleration of the car, we can use the formula for deceleration (a), which is a change in velocity (Δv) divided by the time (t) over which the change occurs. The car is initially moving at 20 m/s and comes to rest, so the change in velocity is -20 m/s (the negative sign indicates a decrease in speed). The time taken to come to rest is 1.8 s. Applying the formula gives us:
Deceleration (a) = Δv / t = -20 m/s / 1.8 s = -11.11 m/s²
The car's deceleration is 11.11 m/s².