A boat of mass \(m\) coasts along a straight horizontal line on a calm lake. At time \(t = 0\), the engine is turned off when the boat has an initial speed \(v_0\). The boat experiences a drag force from the water of magnitude \(F_d = b v^2\), where \(b\) is a positive constant and \(v\) is the speed of the boat. Which of the following expressions gives the speed \(v(t)\) of the boat as a function of time \(t\) for \(t \ge 0\)?