Cart 2 of mass \(2m\) and Cart 1 of mass \(m\) are placed on a horizontal, frictionless track and held together at rest. At time \(t_0\), an internal spring-loaded plunger between them is released, pushing the carts apart until they separate at time \(t_1\). Cart 1 moves in the positive \(x\)-direction after separation. Which of the following graphs best represents the momentum \(p\) of Cart 1 (solid line) and the momentum \(p\) of Cart 2 (dashed line) as functions of time \(t\)?