Math Problem Statement

A veterinarian uses a hypodermic syringe like the one shown in the figure to inject a horse with a medical solution with a density that is the same as water. The barrel of the syringe has a cross-sectional area of 2.63  10-5 m2 and before she exerts any force on the plunger, the pressure everywhere in the syringe is 1.00 atm. When she exerts a force with a magnitude of 2.30 N on the plunger, the medical solution squirts horizontally from the needle. Determine the speed of the solution as it leaves the needle. m/s

Solution

To solve the problem, we use the principles of fluid dynamics, specifically Bernoulli’s equation and the continuity equation. Here’s a detailed breakdown:


Step 1: Bernoulli’s Equation

Bernoulli’s equation states: P1+12ρv12+ρgh1=P2+12ρv22+ρgh2P_1 + \frac{1}{2} \rho v_1^2 + \rho g h_1 = P_2 + \frac{1}{2} \rho v_2^2 + \rho g h_2 Since the liquid exits horizontally and there’s negligible height difference, the terms involving ghg h cancel out. Additionally, the liquid starts at rest inside the syringe, so v10v_1 \approx 0. The equation simplifies to: P1=P2+12ρv22P_1 = P_2 + \frac{1}{2} \rho v_2^2 Rearranging to solve for v2v_2, the speed of the liquid exiting the needle: v2=2(P1P2)ρv_2 = \sqrt{\frac{2 (P_1 - P_2)}{\rho}}


Step 2: Calculate Pressure Difference

The force FF applied to the plunger creates an additional pressure in the syringe: Papplied=FAP_\text{applied} = \frac{F}{A} where:

  • F=2.30NF = 2.30 \, \text{N}
  • A=2.63×105m2A = 2.63 \times 10^{-5} \, \text{m}^2

Substituting: Papplied=2.302.63×105=8.75×104PaP_\text{applied} = \frac{2.30}{2.63 \times 10^{-5}} = 8.75 \times 10^4 \, \text{Pa}

The total pressure inside the syringe becomes: P1=Patm+PappliedP_1 = P_\text{atm} + P_\text{applied} P1=1.00atm+8.75×104PaP_1 = 1.00 \, \text{atm} + 8.75 \times 10^4 \, \text{Pa} Converting 1.00atm1.00 \, \text{atm} to Pascals (1atm=1.013×105Pa1 \, \text{atm} = 1.013 \times 10^5 \, \text{Pa}): P1=1.013×105+8.75×104=1.888×105PaP_1 = 1.013 \times 10^5 + 8.75 \times 10^4 = 1.888 \times 10^5 \, \text{Pa}

The pressure at the exit (P2P_2) is atmospheric pressure: P2=1.013×105PaP_2 = 1.013 \times 10^5 \, \text{Pa}

The pressure difference is: ΔP=P1P2=1.888×1051.013×105=8.75×104Pa\Delta P = P_1 - P_2 = 1.888 \times 10^5 - 1.013 \times 10^5 = 8.75 \times 10^4 \, \text{Pa}


Step 3: Solve for Speed v2v_2

The density of the solution is the same as water (ρ=1000kg/m3\rho = 1000 \, \text{kg/m}^3). Substituting into the velocity equation: v2=2ΔPρv_2 = \sqrt{\frac{2 \Delta P}{\rho}} v2=2(8.75×104)1000v_2 = \sqrt{\frac{2 (8.75 \times 10^4)}{1000}} v2=17513.23m/sv_2 = \sqrt{175} \approx 13.23 \, \text{m/s}


Final Answer:

The speed of the solution as it leaves the needle is approximately: 13.2m/s\boxed{13.2 \, \text{m/s}}


Would you like further clarification or more examples?

Related Questions:

  1. How does the viscosity of the liquid affect the flow rate in this scenario?
  2. What assumptions were made in this calculation, and how could they impact the result?
  3. How would the speed change if the cross-sectional area of the plunger was doubled?
  4. What is the relationship between the applied force and the exit speed of the liquid?
  5. How does Bernoulli’s equation apply to non-horizontal fluid movement?

Tip:

Always ensure consistent units throughout calculations to avoid errors in pressure or velocity evaluations!

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Math Problem Analysis

Mathematical Concepts

Fluid Dynamics
Bernoulli's Equation
Pressure and Force Relationships

Formulas

Bernoulli's equation: P1 + 1/2ρv1² + ρgh1 = P2 + 1/2ρv2² + ρgh2
Pressure due to force: P_applied = F/A
Velocity of fluid: v2 = sqrt(2ΔP / ρ)

Theorems

Bernoulli's Principle

Suitable Grade Level

Undergraduate Physics or Advanced High School Physics