# NCERT Class 11 Physics Solutions: Chapter 10 – Mechanical Properties of Fluids-Part 7

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Question 10.15:

Figures refer to the steady flow of a (non-viscous) liquid. Which of the two figures is incorrect? Why?

Where, Area of pipe

Area of pipe

Speed of the fluid in pipe

Speed of the fluid in pipe

From the law of continuity, we have:

When the area of cross-section in the middle of the venturimeter is small, the speed of the flow of liquid through this part is more. According to Bernoulli’s principle, if speed is more, then pressure is less.

Pressure is directly proportional to height. Hence, the level of water in pipe is less. Therefore, figure is not possible.

Question 10.16:

The cylindrical tube of a spray pump has a cross-section of one end of which has fine holes each of diameter. If the liquid flow inside the tube is , what is the speed of ejection of the liquid through the holes?

Area of cross-section of the spray pump,

Number of holes,

Diameter of each hole,

Area of cross2section of each hole,

Total area of holes,

Speed of flow of liquid inside the tube

Speed of ejection of liquid through the holes

According to the law of continuity, we have:

Therefore, the speed of ejection of the liquid through the holes is

Question 10.17:

U-shaped wire is dipped in a soap solution, and removed. The thin soap film formed between the wire and the light slider supports a weight of (which includes the small weight of the slider). The length of the slider is . What is the surface tension of the film?