Final answer:
The car's average acceleration, when it goes from 40 m/s to a complete stop in 5 seconds, is -8 m/s², which indicates a deceleration of 8 m/s².
Step-by-step explanation:
To calculate the average acceleration of a car that goes from a velocity of 40 m/s to a complete stop in 5 s, you can use the formula for acceleration, which is Δv/Δt, where Δv is the change in velocity and Δt is the change in time. The car's change in velocity (Δv) is -40 m/s (since it decelerates from 40 m/s to 0 m/s, and we take the stopping velocity as 0 m/s minus the initial velocity of 40 m/s). The time (Δt) taken for this change is 5 s. Therefore, the average acceleration can be calculated as:
a = Δv / Δt
a = (-40 m/s) / 5 s
a = -8 m/s2
The negative sign indicates that the acceleration is in the opposite direction to the motion, which is typical for deceleration. Thus, the car's average deceleration is 8 m/s2.