A 1.6 N force is applied to theplunger of a hypodermic needle. The diameter of t

Question

A 1.6 N force is applied to theplunger of a hypodermic needle. The diameter of the plunger is1.5 cm and that of the needle is0.25 mm. (a) With what force does the fluid leave the needle?
          ________ N (b) What force on the plunger would be needed to push fluidinto a vein where the gauge pressure is 18 mm Hg? Answer for theinstant just before the fluid starts to move.          ________ N

A 1.6 N force is applied to theplunger of a hypodermic needle. The diameter of the plunger is1.5 cm and that of the needle is0.25 mm. (a) With what force does the fluid leave the needle?
          ________ N (b) What force on the plunger would be needed to push fluidinto a vein where the gauge pressure is 18 mm Hg? Answer for theinstant just before the fluid starts to move.          ________ N

Explanation / Answer

If the fluid is incompressible, then the pressure must beconstant.                     P = Fn / An = Fp/Ap                  0r    Fn / [ pi(0.025)2 ]/ 4 = 1.6 / [ pi(1.5)2 ] / 4
substituting and simplifying we get
                                   Fn = ------ N
b) The force on the plunger just before the fluid starts tomove is determined by using the fact that pressure in the vein isthe guage pressure
                                  P = Fp /Ap
                        18mm*133N/m2 =  Fp / [pi (1.5*10-2 )2 ] / 4
substituting and simplifying we get
                                          Fp = ------- N
Solve it

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