Cart 1 of mass \(m\) moves to the right at constant speed \(v_0\) along a frictionless horizontal track from time \(t = 0\) to \(t = t_1\). At \(t = t_1\), Cart 1 collides with and sticks to an identical Cart 2 of mass \(m\), which was initially at rest. The combined carts travel along the horizontal track until \(t = t_2\), when they begin ascending a frictionless incline of constant slope, coming momentarily to rest at \(t = t_3\). Which of the following graphs best represents the total kinetic energy \(K\) of the two-cart system as a function of time \(t\) from \(t = 0\) to \(t = t_3\)?