Incompressible & Compressible Aerodynamics

An object of mass 1 kg is launched with an initial speed of vo into a large tank filled with a viscous liquid. The liquid exerts a resistive force (drag) of the form D = 𝛼v on any object that is moving inside it, where v is the instantaneous speed of the object and 𝛼 = 1 kg/s. If the effect of gravity is ignored, the time taken by the object to slow down to the speed vo/2 is ________ s (rounded off to 2 decimal places). Assume that the tank is sufficiently large for the above deceleration to happen inside the tank.