Question

This image shows the direction of the flow of water through a constricted pipe. Which of the following happens as you move from position A to position B in the water pipe?
A. The pressure of the water increases.
B. The density of the water decreases.
C. The cross section of the water decreases.
D. The velocity of the water decreases.

Answer 1

Answer: option is C: the cross-section of the water decreases.

Explanation:

From the equation of continuity for in-compressible fluids (Bernoulli's equation),

a v = constant

where, a is the area and v is the velocity.

Also, pressure is inversely proportional to the velocity.

$a_Av_A = a_Bv_B$

From the image, area of cross-section at A is greater than at B,

$a_A>a_B$

thus,

$v_A < v_B$

which means the velocity of water at B would increase and pressure of the water decreases. Hence, the correct option is C, i.e. the cross-section of the water decreases.