13. [1pt] Water is flowing in a straight horizontal pipe of variable cross secti
ID: 1387977 • Letter: 1
Question
13. [1pt]
Water is flowing in a straight horizontal pipe of variable cross section. Where the cross-sectional area of the pipe is 4.6X 10-2m2, the pressure is 2.10 X 105 Pa and the velocity is 0.66 m/s. In a constricted region where the area is 7.00X 10-4m2, what is the velocity?
ANSWER: 4.34E+01 m/s
14. [1pt]
What is the pressure (in Pa)? (Assume an ideal fluid)
Answer:
15.[1pt]
During high winds, the atmospheric pressure inside a house may blow off the roof because of the reduced pressure outside. Calculate the force on a square roof of side 22.0 m if the wind speed over the roof is 31.0 m/s.
Answer:
Explanation / Answer
(13)
From equation of continuityA1v1 = A2v2
v2 = A1v1/ A2
v2 = (4.6*10^-2 m^2)(0.66) / (7.0*10^-4m^2)
v2 = 4.34810^1 m/s
Use Bernoulli's equation to calculate pressure
P1 + (1/2)(r)v1^2 =P2 + (1/2)(r)v2^2
where r is density of water
P2=P1 + (1/2)(r)v1^2 - (1/2)(r)v2^2
P2= -7.3*10^5 Pa
(15)
The difference in pressure is
P = (1/2)(1.29 kg/m^3)(31 m/s)^2 = 619.8 Pa
The force acting on the roof is
F = PA
F = (619.8 Pa)(22 m * 22m)
F = 3.0*10^5 N
!
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