A horizontal pipe narrows from a diameter of 10.0 to 5.0 cm. For a nonviscous fluid flowing from the larger diameter to the smaller,
A) the velocity and pressure both increase.
B) the velocity increases and the pressure decreases.
C) the velocity decreases and the pressure increases.
D) the velocity and pressure both decrease.
E) either the velocity or the pressure changes but not both.

Question

Quizplus · Accepted Answer

According to the equation of continuity, the mass flow rate must remain constant at every point in a nonviscous fluid flow. Therefore, as the cross-sectional area decreases in the narrow section of the pipe, the fluid must flow faster to maintain the same mass flow rate. This means that the velocity increases. 
According to Bernoulli's equation, as the velocity of a fluid increases, the pressure decreases. Therefore, the pressure in the narrow section of the pipe will be lower than in the wider section. Therefore, option B is the best choice.

A Horizontal Pipe Narrows from a Diameter of 10