Topic: Fluid Mechanics
A glass tube with a 90° bend is open at both the ends. It is inserted into a flowing stream of oil, with specific gravity 0.9, so that one opening is directed upstream and the other is directed upward. Oil inside the tube is 50 mm higher than the surface of flowing oil. The velocity measured by the tube is, nearly:
- A. $1.99~m/s$
- B. $0.99~m/s$
- C. $2.99~m/s$
- D. $3~m/s$
Answer: B. $0.99~m/s$
Explanation: This device acts as a Pitot tube. The rise of liquid in the tube corresponds to the dynamic pressure head.
$h = \frac{V^2}{2g}$. Here $h = 50~mm = 0.05~m$.
$V = \sqrt{2gh} = \sqrt{2 \times 9.81 \times 0.05} = \sqrt{0.981} \approx 0.99~m/s$.