Final answer:
The value of k that would result in a physically possible flow is k = 1.
Step-by-step explanation:
Flow rate and velocity are related by the equation Q = AU, where A is the cross-sectional area of the flow and U is its average velocity. For incompressible fluids, the flow rate at various points must be constant to ensure continuity of flow. In this case, since the cross-sectional area of the pipe decreases, the velocity must necessarily increase. In order to have a physically possible flow, the value of k should be positive. So the correct value of k in this case would be k = 1 (option a).