Q. 20

# Water is flowing through a long horizontal tube. Let P_{A} and P_{B} be the pressures at two points A and B of the tube.

A. P_{A} must be equal to P_{B}

B. P_{A} must be greater than P_{B}

C. P_{A} must be smaller than P_{B}

D. P_{A} = P_{B} only if the cross-sectional area at A and B are equal.

Answer :

The pressure at the two points would be equal only if the velocities of the water at these points are equal. This is possible only if the cross-sectional areas are equal at the points. If this is not true, the pressure will vary with the velocities of the water at the points.

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