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Homework Help: A simple Fluid Dynamics/Pressure HW question

  1. Apr 21, 2015 #1
    1. The problem statement, all variables and given/known data
    A piston of cross-sectional area a is used in a hydraulic press to exert a small force of magnitude f on the enclosed liquid. A connecting pipe leads to a larger piston of cross-sectional area A (the figure). If the piston diameters are 3.63 cm and 50.7 cm, what force magnitude on the small piston will balance a 41.8 kN force on the large piston?

    2. Relevant equations

    3. The attempt at a solution
    So I'm pretty sure I'm doing this right especially since we did a similar one in class so I think it might just be a math error here's what I did.

    For the smaller side Ps = Fs/as

    For the larger side Pb = Fb/Ab

    Ps = Pb

    Fs/as = Fb/Ab

    Solve for Fs
    Fs = Fb/Ab * as

    Plug in values (Fb 41.8kN = 41800N) (Ab 50.7cm =.507m) (as 3.63cm = .0363m)

    Fs = (41800/.507)*.0363 = 2992.78N WileyPlus says its wrong though, so did I make a mistake?

    Attached Files:

    Last edited: Apr 21, 2015
  2. jcsd
  3. Apr 21, 2015 #2
    For some reason you plugged in the diameters instead of the areas.
  4. Apr 21, 2015 #3
    I guess I did. I didn't even notice it said diameters thanks. I must remember to read more thoroughly next time.
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