Water (density = 1 × 103 kg/m3) flows at 10 m/s through a pipe with radius 0.025 m. The pipe goes up to the second floor of the building, 2.5 m higher, and the pressure remains unchanged. What is the radius of the pipe on the second floor?Select one:a.0.187 mb.0.011 mc.0.03 md.0.001 me.0.023 m
Question
Water (density = 1 × 103 kg/m3) flows at 10 m/s through a pipe with radius 0.025 m. The pipe goes up to the second floor of the building, 2.5 m higher, and the pressure remains unchanged. What is the radius of the pipe on the second floor?Select one:a.0.187 mb.0.011 mc.0.03 md.0.001 me.0.023 m
Solution
To solve this problem, we can use the principle of continuity which states that the volume flow rate must be the same at all points along the pipe. The volume flow rate is given by the equation Q = Av, where A is the cross-sectional area of the pipe and v is the velocity of the water.
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First, calculate the cross-sectional area of the pipe on the first floor using the formula A = πr², where r is the radius of the pipe.
A1 = π(0.025 m)² = 0.00196 m²
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Then, calculate the volume flow rate on the first floor using the formula Q = Av.
Q1 = A1 * v1 = 0.00196 m² * 10 m/s = 0.0196 m³/s
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The volume flow rate on the second floor must be the same as on the first floor, so Q2 = Q1 = 0.0196 m³/s.
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We can find the velocity on the second floor using Bernoulli's equation, which states that the sum of the pressure energy, kinetic energy, and potential energy per unit volume is constant along a streamline. Since the problem states that the pressure remains unchanged, the increase in potential energy must be balanced by a decrease in kinetic energy.
The potential energy per unit volume is given by ρgh, where ρ is the density of the water, g is the acceleration due to gravity, and h is the height difference.
ΔPE = ρgh = (1 × 10³ kg/m³)(9.81 m/s²)(2.5 m) = 2.4525 × 10⁴ J/m³
The kinetic energy per unit volume is given by ½ρv², so the change in kinetic energy is ΔKE = ½ρ(v1² - v2²).
Setting ΔPE = ΔKE and solving for v2 gives v2 = sqrt(v1² - 2gh) = sqrt((10 m/s)² - 29.81 m/s²2.5 m) = 7.67 m/s.
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Finally, we can find the cross-sectional area on the second floor using the formula A = Q/v.
A2 = Q2 / v2 = 0.0196 m³/s / 7.67 m/s = 0.00256 m²
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And the radius on the second floor using the formula r = sqrt(A/π).
r2 = sqrt(0.00256 m² / π) = 0.0285 m
So, the radius of the pipe on the second floor is approximately 0.0285 m. This is closest to option c. 0.03 m.
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