Determine the medicine's flow speed through the needle

In summary, a hypodermic syringe with a medicine of the same density as water has a cross-sectional area of 2.20 10-5 m2 and experiences a pressure of 1.00 atm when no force is applied to the plunger. When a force of 1.80 N is applied to the plunger, the medicine squirts from the needle at a flow speed that can be determined using Bernoulli's equation and the continuity equation. The pressure in the needle remains at 1.00 atm and the syringe is horizontal.
  • #1
LesVampires
13
0
A hypodermic syringe contains a medicine with the density of water (see figure below). The barrel of the syringe has a cross-sectional area of 2.20 10-5 m2. In the absence of a force on the plunger, the pressure everywhere is 1.00 atm. A force of magnitude 1.80 N is exerted on the plunger, making medicine squirt from the needle. Determine the medicine's flow speed through the needle. Assume the pressure in the needle remains equal to 1.00 atm and that the syringe is horizontal.

second question

An 11.3 kg block of metal is suspended from a scale and immersed in water, as in the figure below. The dimensions of the block are 12.0 cm 8.7 cm 8.7 cm. The 12.0 cm dimension is vertical, and the top of the block is 5.00 cm below the surface of the wateri know that P=Po + pgh p=m/v and g i can't figure h out
can u direct me a bit with this ty verymuch

Homework Statement


Homework Equations


The Attempt at a Solution

 
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  • #2
LesVampires said:
A hypodermic syringe contains a medicine with the density of water (see figure below). The barrel of the syringe has a cross-sectional area of 2.20 10-5 m2. In the absence of a force on the plunger, the pressure everywhere is 1.00 atm. A force of magnitude 1.80 N is exerted on the plunger, making medicine squirt from the needle. Determine the medicine's flow speed through the needle. Assume the pressure in the needle remains equal to 1.00 atm and that the syringe is horizontal.

http://www.princeton.edu/~asmits/Bicycle_web/Bernoulli.html

height stays same so it cancels

solve for v
 
  • #3
hmm i know that Av= Av and the equations but i keep gettin a wrong answer... A= 2.2x10^-5 m^2
 
  • #4
LesVampires said:
hmm i know that Av= Av and the equations but i keep gettin a wrong answer... A= 2.2x10^-5 m^2

[tex] P_1 + 1/2 \rho v^2 + \rho gy_1 = P_2 + 1/2\rho v^2 + \rho g y_2 [/tex]

don't forget atmospheric pressure is at the end of the needle solve for v2

P=F/A to find the pressure exerted over the area of the plunger (force exerted on plunger )

After finding the equivalent pressure that is due to the plunger, add that to atm pressure.

show me what you did and I'll tell you what your doing incorrect.
 
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  • #5
well the pgys are 0 u have v= 2change in P/pv pv is A right? P=1.01 x10^5 and
 
  • #6
LesVampires said:
well the pgys are 0 u have v= 2change in P/pv pv is A right? P=1.01 x10^5 and


yes pgy is 0 so what is the equation then?

not sure what your saying when you say
v=2change in P/pv pv is A
:confused:


and the area is small on the end of the syringe but did they give it to you?


Look at the post above (last post by me) I added stuff.

I have to go but I'll see what you did tommorow (post your work)

A2/A1<<1 -> note
 
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  • #7
isnt that what's left of the equation?
 
  • #8
LesVampires said:
isnt that what's left of the equation?

what are you talking about.

No the A1V1=A2V2 is the continuity equation and that is substituted into the bernoulli equation. And then you can solve for v2 which you want.
 

1. How is the flow speed of a medicine through a needle determined?

The flow speed of a medicine through a needle is determined by measuring the volume of medicine that flows through the needle in a certain amount of time. This can be done using a stopwatch and a graduated cylinder or by using specialized equipment such as a flow meter.

2. What factors can affect the flow speed of a medicine through a needle?

The flow speed of a medicine through a needle can be affected by several factors, including the viscosity of the medicine, the gauge and length of the needle, the pressure applied to the syringe, and any obstructions in the needle or syringe.

3. Why is it important to determine the flow speed of a medicine through a needle?

Knowing the flow speed of a medicine through a needle is important for ensuring accurate dosing and proper administration of the medicine. It can also help to identify any potential issues or blockages in the needle or syringe that may affect the effectiveness of the medicine.

4. What units are typically used to measure the flow speed of a medicine through a needle?

The flow speed of a medicine through a needle is typically measured in milliliters per second (mL/s) or milliliters per minute (mL/min). In some cases, it may also be measured in drops per minute (dpm) for smaller volumes of medicine.

5. Are there any safety precautions to keep in mind when determining the flow speed of a medicine through a needle?

Yes, there are several safety precautions to keep in mind when determining the flow speed of a medicine through a needle. These include wearing appropriate protective gear, such as gloves and goggles, to prevent contact with the medicine, and following proper disposal procedures for any used needles or syringes.

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