A tank is full of oil weighing 30 lb/ft3. The tank is a right rectangular prism with a width of 2 feet, a depth of 2 feet, and a height of 3 feet. Find the work required to pump the water to a height of 2 feet above the top of the tank

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Answer:

the work will be W= 17373.96 lb*ft²/s²

Step-by-step explanation:

Neglecting the frictional losses in the pipe and the pump efficiency, then assuming a reversible process the work W will be

W= ∫pdV

from an energy balance (see note below), and assuming constant density of the oil, the pressures at pump output and pump input will be

P final = p₀ + ρ*g*h = p₀ + ρ*g*h + 1/2ρ*v²

P initial =  p₀ + 1/2ρ*v²

where

p₀= pressure at the surface

ρ= density

g= gravity

h= height of the oil level

the volume of pumped oil will be

V= A*h

dV=A*dh

then the pressure the pump has to work against is:

p= Pfinal- Pinitial = ρ*g*h

therefore

W=∫pdV = A∫ρ*g*h*dh = A*ρ*g*H²/2 = ρ*g*V*H/2

replacing values

V= 2 ft* 2 ft * 3 ft = 12 ft³

W= ρ*g*V*H/2= 30 lb/ft³* 32.174 ft/s²* 12 ft³ * 3 ft/2 = 17373.96 lb*ft²/s²

W= 17373.96 lb*ft²/s²

Note

- from mass conservation at the bottom of the tank and pump output

Apipe*vpipe = Apump*vpump

assuming that the discharge pipe has the same pipe diameter then Apump= Apipe → vpipe= vpump=v

- the final work is the average of the work for a completely charged tank and with almost any oil (H=0)  ( assuming no suction of air/vapor with low oil levels)

The work required to pump the water to a height of 2 feet above the tank is 975.51 J.

To calculate the work required to pump the oil to a height of 2 feet above the top of the tank, we use the formula below.

Formula:

  • W = mgh............................. Equation 1

Where:

  • W = Work required to pump the water
  • m = mass of the oil
  • d = height.
  • g = acceleration due to gravity.

We need to find the mass of the oil, using the formula below.

  • D = m/V
  • m = DV............. Equation 2

From the question,

Given:

  • D = 30 lb/ft³
  • V = 2×2×3 = 12 ft³

Substitute these values into equation 2

  • m = 30(12) = 360 lb
  • m = 163.29 kg

Also,

Given:

  • h = 2 feet = (2×0.3048) m = 0.6096 m
  • g = 9.8 m/s²

Substitute these values into equation 1

  • W = 163.29×9.8×0.6096
  • W = 975.51 J.

Hence, the work required to pump the water to a height of 2 feet above the tank is 975.51 J

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