Question

15. A hypodermic syringe has a 1.0 cm diameter piston, and is connected to a needle of area 0.071 mm². If the needle were inserted into a blood vessel of maximum interior gauge pressure 80.0 mmHg, how much force (in N, minimum) should be exerted on the piston to allow for injection? 16. Continuing with #15, how much inward force acts on the fluid at the needle? (This just equals the outward force from the blood vessel at the threshold for injection.)

Answer 1

15. 80mm of Hg is equal to

P = phg = 0.080 * 13.6 * 103 * 10

P = 10880 Pascal

So as the pressure must be equal to the blood pressure.

$P = \frac{F}{A}$

F = PA= 10880 * 7 *0.012 = 108807 * 0.0001 = 3.418N

16. As per as pascal law, Pressure in a fluid remains constant.

F= PA= 10880*0.071 * 10-6 = 7.7248 * 10-