Answer:
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!
