Question

A liquid is flowing in a cylindrical pipe of internal diameter 4 cm with a velocity of 5m s${}^{-1}$. If this tube is joined with another tube of internal diameter 2cm then the velocity of flow of liquid in the smaller tube will be ( in ms${}^{-1}$)

• A. 10
• B. 40
• C. 5
• D. 20

Answer 1

Answer: (D)

20

$A_1{V}_1=A_2{V}_2$

$\pi r_1^2{V}_1=\pi r_2^2{V}_2$
$\Rightarrow V_2={\left(\frac{r_1}{r_2}\right)}^2{V}_1$$={\left(2\right)}^2{V}_1=4\times 5=20m{s}^{-1}$