Label distance between AB, BC and CD. The choices are :
Constant acceleration.
Decreasing acceleration.
Increasing acceleration.
Moving backwards at constant speed.
Moving forward at constant speed.
Stationary.

AB: decreasing acceleration

BC: constant acceleration

CD: constant acceleration.

Explanation:

(1) Here is the plot of velocity and time.

There is no information of distance.

=>  There are two options that will be eliminated.

Moving backwards at constant speed.

Moving forward at constant speed.

(2) Only for remaining options will be considered:

Constant acceleration.

Decreasing acceleration.

Increasing acceleration.

Stationary.

(3) The formula for calculating final velocity:

v_final = v_initial + acceleration x time

Let's see BC: (this is a segment straight line)

v_C = v_B + acceleration x time

v_C = v _B = 40 (km/h)

time > 0

=> acceleration a = 0 (km/h^2) => constant acceleration

Let's see CD: (this is also a segment straight line)

v_D = v_C + acceleration x time

v_D = 0 (km/h)

v_C = 40 (km/h)

time > 0

=> acceleration = -40/time (km/h^2) < 0 => constant (negative) acceleration

Let's see AB (a segment straight line + a right curve)

On the segment straight line:

Using the same way we considered CD,

the acceleration is constant (positive) acceleration

On the right curve (with direction from A to B), its slope started to decrease. This slope is the change of acceleration.

=> Generally on AB (considering both segment straight line and the right curve), the acceleration is decreasing acceleration

P.S: Take the derivative of v_final with respect to acceleration a, plot a as a function of time , then you will see what really happened ^^.

Hope this helps!

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