JEE Advanced 2020 Physics question
A train with cross-sectional area is moving with speed inside a long tunnel of cross-sectional area . Assume that almost all the air (density ) in front of the train flows back between its sides and the walls of the tunnel. Also, the air flow with respect to the train is steady and laminar. Take the ambient pressure and that inside the train to be . If the pressure in the region between the sides of the train and the tunnel walls is , then . The value of is .
Solution
Work in the frame of the train, where the flow is steady. Far ahead of the train the air approaches with speed through the full area at pressure . It passes the train through the annular area with speed . Continuity: $ = -
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