Question

At the mouth of the tap, the area of cross-section is $2.0c{m}^2$ and the speed of water is $3m/s$. The area of cross-section of the water column $80cm$ below the tap is $(useg=10m/s^2)$

• A. $0.6c{m}^2$
• B. $1.2c{m}^2$
• C. $1.5c{m}^2$
• D. $2.0c{m}^2$

Answer 1

The correct option is B $1.2c{m}^2$

area of cross section at mouth $A_1=2\times {10}^{-4}{m}^2$

velocity $V_1=3m/s$

$80cm$ below the mouth of the tap,

velocity of water

$80cm$ below the mouth of the tap,

velocity of water

$V_2^2=V_1^2+2gh,h=0.8m$

or $V_2^2=9+2\times 10\times 0.8$

or $V_2^2=9+16$

or $V_2=5$

flow of water per unit volume $=$ constant

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

$2\times {10}^{-4}\times 3=A_2\times 5$

or $A_2=1.2\times {10}^{-4}{m}^2=1.2c{m}^2$

Ans. - Option-B