1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Syringe find min force

  1. Jun 10, 2009 #1
    A syringe with a plunger of diameter 2 cm is attached to a hypodermic needle with a diameter of 2.1 mm. What minimum force (in N) must be applied to the plunger to inject into a vein where the pressure is 16 torr above atmospheric pressure.

    P=F/A since P will be constant throughout F/Aplunger= F/A vein

    First 760torr=1 atm=1.01*10^5N/m^2, which gave me the pressure in the vein =2126.3. Then I said that P, which is 2126.3* area of the plunger (pi*r^2)
    2126.3*pi*(.002)^2=.00668 which sound be by answer- the F. Although this is not correct. Where am I going wrong?
  2. jcsd
  3. Jun 10, 2009 #2


    User Avatar
    Homework Helper

    Check too to see that you are using radius and not diameters.

    Diameter of 2 cm means radius or 1 cm = .01 m.
  4. Jun 11, 2009 #3
    Thanks- that was why I was incorrect.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook