A conducting bar of mass \(m\) and resistance \(R\) slides without friction along two parallel horizontal conducting rails separated by distance \(L\). The rails are connected at one end through an ideal resistor of resistance \(R\), forming a closed circuit in a uniform magnetic field \(\vec{B}\) directed perpendicular to the plane of the rails. At time \(t = 0\), the bar is launched to the right with an initial velocity \(v_0\). At time \(t = t_1\), while the bar is still moving, the magnitude of the magnetic field is instantaneously doubled from \(B_0\) to \(2B_0\). Which of the following graphs best represents the velocity \(v\) of the bar as a function of time \(t\)?