ANS:B - long pipe at decreasing rate.

Unsteady uniform flow is represented by flow through a long pipe at constant rate. Here's an explanation of each option:

• Long pipe at constant rate: Unsteady uniform flow occurs when the flow rate through a long pipe remains constant over time, but the flow parameters (such as velocity and pressure) change with respect to time. This could be due to variations in boundary conditions or disturbances in the flow.
• Long pipe at decreasing rate: This would typically indicate a transient flow situation where the flow rate is changing over time, not unsteady uniform flow.
• Expanding tube at increasing rate: Flow through an expanding tube generally involves changing cross-sectional areas, which complicates the definition of uniform flow. Moreover, if the rate of flow is increasing, it usually indicates a transient or non-uniform flow scenario.
• Expanding tube at constant rate: Similar to above, the variation in cross-sectional area makes it challenging to maintain uniform flow conditions over time.