Question

Fire is caught at height of 125 m from the fire brigade. To extinguish the fire, water is coming out from the pipe of cross section 6.4 cm with rate 950 litre/ min. Find out minimum velocity of water existing from fire brigade tank. $(g=10m/s^2)$:

• A. 5 m/s
• B. 10 m/s
• C. 25 m/s
• D. 50 m/s

Answer 1

Answer: (A)

5 m/s

Rate of flow = Area of cross section $\times$ velocity = which is same everywhere

Given$:$

R (Rate of flow) $=950\frac{L}{min}=950\frac{{10}^{-3}{m}^3}{60sec}=\frac{95}{6}\times {10}^{-3}\frac{m^3}{s}$

Radius of pipe $=\frac{6.4}{2}cm=0.032m$

A (Area of cross section) $=\pi \times {\left(0.032\right)}^2{m}^2$

We Know,

R = A $\times$ V

V (Velocity) $=\frac{R}{A}$

$=4.92m/s=5m/s(approx.)$