Answer
(e) All A, B and C could describe the motion of the RV.
Work Step by Step
Let's examine each of the situations.
A) When the RV is at rest, the cup is also at rest. Then the driver suddenly accelerates the RV, but there is no force exerted on the cup to accelerate it too. So according to Newton's 1st law, the cup continues to be at rest. Since all the interior of the RV moves forward while the cup remains at rest, it slides towards the rear of the RV as a result.
B) When the RV is moving forward with speed $v_0$, the cup also has speed $v_0$.
The driver accelerates with a rate of $a$ over time $t$, the new speed of the RV is $v_0+at$. Yet, since there is no force propelling the cup, its speed remains $v_0$.
The interior of the car therefore moves faster than the cup, leaving it sliding back to the rear.
C) The RV and the cup are both moving backward. However, the driver brakes and the RV is decelerated to a halt. The cup is not affected by the brake and continues to move backward following Newton's 1st law. As a result, the cup will slide towards the rear.
Therefore, all A, B and C could describe the motion of the RV.
