in the figure why have we taken speicifc weight of water at the end even though
ID: 1793734 • Letter: I
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in the figure why have we taken speicifc weight of water at the end even though pressure p1 is due to air so we should take specific weight of air
EXAMPLE 6.4 A closed tank partially filled with water up to a height of 1m, having an orifice of diameter 20 m at the bottom of the tank. Determine the pressure required for a discharge of 3.0 litres through the orifice. Take cd 0.62. Solution : Given H= 1 m d=20 mm = 0.02 m Water Q=31/s = 100 m3/s Cd0.62 0.003 m 1m 0.003 velocity ofjet, u=axdT(0.02)2 x0.62 Consider two points 1 and 2. Point 1 is on the free water surface and point 2 is on the Applying Bernoulli's equation at 1 and 2, we get = 15.40 m/s FIG. 6.9 outlet u) u = 15.40 m/s 2.-1.0m ORIFICE AND MOUTHPIECE Applying Bernoulli's equation at 1 and 2, we get tD 215.40 m/s 21 = 1.0 m Let p be the pressure required Equation (1) becomes 15.402 2x9.81 +0+1-0+ +0 P+1 12.09 = 12.09-1-11.09 p= 11.09 w= 11.09 9810=108792.9 N/m2 Ans.Explanation / Answer
Yes , you are right , Pressre is due to air but see the Bernoulli's theorem where we divide the , pressure exerted on liquid with specific weight of liquid (w) , that's why we have put the specific weight of liquid ... You are looking at final step but how we reach there , that is using Bernoulli's theorem where , w is specific of liquid on which therome is applying
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