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**Question 1: ****Water is pumped steadily out of a flooded basement at a speed of 5.30 m/s through a uniform hose of radius 9.70 mm. The hose passes out through a window 2.90 m above the water line. How much power is supplied by the pump?****Concept:-**

The kinetic energy of the water per unit mass when it leaves from the uniform hose through the window is

K = ½ v^{2}

Here, mass of the flow of water is and speed of the water flow is v.

The corresponding potential energy per unit mass of the flow of water through the window is

U = gh

Here, acceleration due to gravity of the Earth is g and height of the window from the basement is h.

The volume rate of the flow of water from the hose through the window is

R = vA

Here, cross-sectional area of the hose is A and speed of the water flow is v.

The mass rate of the flow of water is

R_{m} = ρR

Here, density of the water is ρ.

The power supplied by the pump is given by

P = (K+U) R_{m}**Solution**:-

The cross-sectional area of the hose is

A = πr^{2}

Here, radius of the hose is r.

Insert the values of in the equation R = vA gives

R = v (πr^{2})

Using the above values in the equation Rm = ρR

gives

Rm = ρv (πr^{2})

Substitute the values of K, U and Rm in the equation P = (K+U) Rm gives

P = [(1/2) v^{2} + gh] [ρv (πr^{2})]

To obtain the power supplied by the pump, substitute 5.30 m/s for v, 9.8 m/s^{2} for g, 2.90 m for h, 1000 kg/m^{3} for ρ and 9.70 mm for r in the above equation gives

P = [(1/2) v^{2} + gh] [ρv (πr^{2})]

= [(1/2) (5.30 m/s)^{2} + (9.8 m/s)^{2} (2.90 m)] [(1000 kg/m^{3}) (5.30 m/s) (3.14) (9.70 mm)^{2} (10^{-3} m/1 mm)^{2}]

= (14.045 m^{2}/s^{2} + 28.42 m^{2}/s^{2}) (1.56584578 kg/s)

= (66.494 kg.m^{2}/s) [1 W/(1kg.m^{2}/s)]

= 66.494 W

Rounding off to three significant figures, the power supplied by the pump is 66.5 W.

**Question 2: ****A hollow tube has a disk DD attached to its end as shown in the below figure. When air of density ρ is blown through the tube, the disk attracts the card CC. Let the area of the card be A and let v be the average air speed between the card and the disk. Calculate the resultant upward force on CC. Neglect the card’s weight; assume that v _{0}<<v, where v_{0} is the air speed in the hollow tube.**

According to Bernoulli’s equation, the total energy of the steady flow of air in the hollow tube remains constant.

It is given as

p+ ½ ρv

Here, pressure of the flow of air is p, density of the air is ρ, speed of the air in the hollow tube is v, acceleration due to gravity of the earth at the point of observation is g and position of the flow of air from the ground is h.

The resultant upward force on the card CC is equal to the difference in the pressure times the area of the card CC.

Apply Bernoulli’s equation just before it leaves the hollow tube, the total energy of the flow of air is

p

Here, pressure of the flow of air just before it leaves the hollow tube is p1, speed of the air in the hollow tube is v0, and position of the flow of air from the ground before the air leaves the hollow tube is y1.

On the upper surface of the card CC, the total energy of the flow of air is

p

Here, pressure of the flow of air above the car CC is p

The total energy for the flow of air remains the same when it flows from the hollow tube to the card CC.

Thus,

p

The position of the flow of air is same for the same flow of air.

Thus,

y1 = y2

Also, it is given that v

So, the speed in the hollow tube v

Insert y

Gives

p

p

Now, the resultant upward force on the card CC is

F = (p

Substitute ½ ρv

F = (p

= ½ ρv

Therefore, the resultant upward force on the CC is ½ ρv

**Question 3:**** A siphon is a device for removing liquid from a container that is not to be tipped. It operates as shown in below figure. The tube must initially be filled, but once this has been done the liquid will flow until its level drops below the tube opening at A. The liquid has density ρ and negligible viscosity. (a) With what speed does the liquid emerge from the tube at C? (b) What is the pressure in the liquid at the topmost point B? (c) What is the greatest possible height h that a siphon may lift water?****Concept:-**

From Torricelli’s law, the speed of the water emerges from a depth h through a hole in a tank is

v =√2gh

Here, acceleration due to gravity is g.

The pressure at the depth h is

p = p_{0}+ρgh

Here, pressure at the surface of the water is p0 and density of the water is ρ.**Solution**:-

(a) Water will flow in the pipe and emerges from the point C. It is considered that water flows from depth equal to the d+h_{2}.

Here, the equivalent depth of the water is

h = d+ h_{2}

From equation v =√2gh, the speed of the water is

v =√2gh

=√2g(d+h_{2})

Therefore, the speed of the water emerges from the point C is √2g(d+h_{2}).

(b) The pressure at the point C is

p_{C} = ρg (h_{1}+d+h_{2})

Now, the pressure at the point B is

p_{B} = p0 – p_{C}

Insert p_{C }= ρg (h_{1}+d+h_{2}) in the above equation gives

p_{B} = p_{0} – p_{C}= p_{0 }- ρg (h_{1}+d+h_{2})

Therefore, the pressure at the point B is p_{0} - ρg (h_{1}+d+h_{2}).

(c) Now, the maximum possible height is obtained as

p_{0 }= ρgh

h = p_{0}/ρg

Substitute 1.01×105 kg/m.s^{2} for p_{0}, 1000 kg/m^{3} for ρ and 9.8 m/s^{2} for g in the above equation gives

h = p_{0}/ρg

= (1.01×10^{5} kg/m.s^{2})/( 1000 kg/m^{3}) (9.8 m/s^{2})

= 10.306 m

Rounding off to three significant figures, the greatest possible height that the siphon may lift water is 10.3 m

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