## Question

### Solution

Correct option is

20 m/s

According to Bernoulli’s theorem, we have  Here v1 = 0 (the valve is initially closed, and so the velocity of water is zero). .

Here (for water)   = 400 m2/s2

or       v2 = 20 m/s.

#### SIMILAR QUESTIONS

Q1

The critical velocity of an oil drop in air is . What is the radius of the drop? If two such drops coalesce than what will be the terminal velocity of the resultant drop. Coefficient of viscosity of oil is and density is . The density of air in comparison to oil is negligible and .

Q2

A metal sphere of diameter enters water after falling a distance h freely in the gravitational field of the earth. After entrance in water, its velocity remains unchanged. Calculate the value of h. The coefficient of viscosity of water , density of water and acceleration due to gravity = 10 N/kg.

Q3

An air bubble of radius 1.0 mm rises with uniform velocity through a viscous liquid of density 1625 kg/m3. Calculate the velocity of the bubble if the coefficient of viscosity of the liquid is 10 poise and the density of air is negligible. (g = 10 m/s2).

Q4

An air bubble of radius 0.1 mm is moving upwards in water with a velocity of 0.35 cm/s. If the density of water is and gravitational acceleration is 9.8 m/s2 and the density of the air is negligible, then find out the coefficient of viscosity of water.

Q5

A small sphere falls from rest under gravity in a viscous medium, producing heat due to friction. Find how rate of production of heat does depend upon the radius of the sphere at terminal velocity.

Q6

Water at a pressure of flows at 2.0 m/s through a pipe of 0.02 m2 cross-sectional area which reduces to 0.01 m2. What is the pressure in the smaller in the cross-section of the pipe?

Q7

Water is flowing through two horizontal pipes of different diameters which are connected together. In the first pipe the speed of water is 4.0 m/s and the pressure is . Calculate the speed and pressure of water in the second pipe. The diameters of the pipes are 3.0 cm and 6.0 cm respectively.

Q8

A liquid is kept in a cylindrical vessel which is being rotated about its axis. The liquid rises at the sides. If the radius of the vessel is 0.05 m and the speed of rotation is 2 rev/s, find the difference in the heights of liquid at the centre of the vessel and at its sides. Q9

The pressure difference between two points along a horizontal pipe, through which water is flowing, is 1.4 cm of mercury. If, due to non-uniform cross-section, the speed of flow of water at the point of greater cross-section is 60 cm/s, calculate the speed at the other point. Density of mercury .

Q10

Air is streaming past a horizontal aeroplane wing such that its speed is 120 ms–1 at the upper surface and 90 ms–1 at the lower surface. If the density of air is 1.3 kg/m3, find the difference in pressures between the two surfaces of the wing. If the wing is 10 m long and has an average width of 2 m, then calculate the gross lift on it.