Question

Please answer with full explanation as to why thank you.

1) A group of water particles move together in river, the sum of all forces on their boundary must be zero, (True or False)?

2) water flow in a pipe from reservoir  and its gate is open initially. when the gate is suddenly closed, the pressure change in front of gate increases with

(a) water speed

(b) pipe diameter

(c) water density

Answer 1

1. Statement ios True.

forces acting on particles in horizontal direction at boundary are 1. tractive force ( due to momentum), 2. frictional force. Both are in opposite direction so cancelled each other at boundary. but as we moved up (away from boundary) friction force decreases rate flow is increases as we move up. So velocity at top is high in revers and as we do down velocity decrease.

2. (a) pressure is inversely proportional water speed (deduced by bernaulli's equation). so infront of gate pressure increase with decrease in velotiy.