What is the velocity of medicine emerging from a hypodermic syringe?

AI Thread Summary
The discussion focuses on calculating the velocity of medicine emerging from a hypodermic syringe, given specific parameters such as the syringe's cross-sectional area and the force applied to the plunger. The initial pressure inside the syringe is determined to be 80,000 Pascals, calculated using the force and area. As the area decreases, the velocity of the medicine increases, leading to a decrease in pressure, which raises the question of why the pressure outside the syringe is assumed to be zero. The pressure inside the syringe combines atmospheric pressure with the pressure from the applied force, while the outside pressure is solely atmospheric. The conversation emphasizes the relationship between pressure and velocity in fluid dynamics as it applies to the syringe's operation.
rawimpact
Messages
14
Reaction score
0
1. A hypodermic syringe contains a medicine with a density of water. The barrel of the syringe has a cross-sectional area of 2.5x10e-5 m^2. A force of 2N is exerted on the pluger (left, larger side). Determine the velocity of the medicine as it emerges from the needle

_________
\
\
(1) (2)=====
/
_________/

2. P1 + 1/2pV1^2 + pghi = P2 + 1/2pV2^2 + pghf

Area = 2.5x10e-5 m^s, Force = 2 N

P1 = F/A = 80,000 Pascals

Because Area decreases, Velocity increases decreasing pressure so we assume P2 = 0, is this correct why we make P2 = 0?
 
Physics news on Phys.org
Inside the syringe pressure in the liquid is sum of atmospheric pressure and pressure due 2N force. Outside the syringe there is only atmospheric pressure.
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top