Math Problem Statement

A small circular hole 5.00 cm in diameter is cut in the side of a large water tank, 15.0 m below the water level in the tank. The top of the tank is open to the air. Find the speed and the mass flow rate of the water (ρwater = 1000 kg/m³) through the small hole. Assume that the speed of the water at the top of the tank is zero. Hint: The pressure at both holes are equal to Patm.

Solution

This problem involves fluid dynamics and can be solved using Torricelli's Law, derived from Bernoulli's Equation. Here's how we solve it step by step:

Given:

  • Diameter of the hole, d=5.00cm=0.05md = 5.00 \, \text{cm} = 0.05 \, \text{m}
  • Radius of the hole, r=d2=0.025mr = \frac{d}{2} = 0.025 \, \text{m}
  • Height difference, h=15.0mh = 15.0 \, \text{m}
  • Density of water, ρ=1000kg/m3\rho = 1000 \, \text{kg/m}^3
  • Acceleration due to gravity, g=9.8m/s2g = 9.8 \, \text{m/s}^2
  • Atmospheric pressure cancels out since both sides are exposed to it.

Step 1: Find the speed of water (vv) exiting the hole.

From Torricelli’s Law, the speed of water exiting the hole is: v=2ghv = \sqrt{2 g h} Substitute the given values: v=29.815.0v = \sqrt{2 \cdot 9.8 \cdot 15.0} v=29417.15m/sv = \sqrt{294} \approx 17.15 \, \text{m/s}

Step 2: Find the mass flow rate (m˙\dot{m}).

The mass flow rate is given by: m˙=ρAv\dot{m} = \rho \cdot A \cdot v where:

  • AA is the cross-sectional area of the hole: A=πr2=π(0.025)2=π0.0006250.00196m2A = \pi r^2 = \pi (0.025)^2 = \pi \cdot 0.000625 \approx 0.00196 \, \text{m}^2 Substitute into the mass flow rate equation: m˙=10000.0019617.15\dot{m} = 1000 \cdot 0.00196 \cdot 17.15 m˙33.6kg/s\dot{m} \approx 33.6 \, \text{kg/s}

Final Answers:

  1. Speed of water exiting the hole: v17.15m/sv \approx 17.15 \, \text{m/s}
  2. Mass flow rate of water: m˙33.6kg/s\dot{m} \approx 33.6 \, \text{kg/s}

Would you like further clarification or additional details on any part of this solution? Here are some related questions for practice:


  1. How would the speed of water change if the height hh was doubled?
  2. What would happen to the mass flow rate if the diameter of the hole was reduced to 3.00cm3.00 \, \text{cm}?
  3. How does atmospheric pressure influence the result?
  4. What assumptions are we making about the tank in applying Torricelli’s Law?
  5. How would this setup differ if the fluid were oil (ρ=850kg/m3\rho = 850 \, \text{kg/m}^3) instead of water?

Tip: Always check if atmospheric pressure cancels out in fluid flow problems; this can simplify calculations significantly!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Fluid Dynamics
Kinematics

Formulas

Torricelli's Law: v = √(2gh)
Mass Flow Rate: ṁ = ρ * A * v
Area of Circle: A = πr²

Theorems

Bernoulli's Principle

Suitable Grade Level

Grades 11-12