Hydraulic piston break system problem

AI Thread Summary
The discussion revolves around a hydraulic brake system problem involving the calculation of frictional torque based on given parameters. The user initially applies the pressure distribution formula incorrectly, leading to a discrepancy in the calculated force and resulting torque. The correct approach involves using the ratio of the piston areas to determine the force in the brake cylinder, resulting in a frictional torque of 2.1 N*m, as indicated by the answer keys. There is confusion regarding the problem statement and the accompanying diagram, which may have contributed to the misunderstanding. Clarification on the correct method is sought to resolve the calculation error.
Thundagere
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Homework Statement



The figure below shows the essential parts of a hydraulic brake system. The area of the piston in the master cylinder is 1.8 cm2, and that of the piston in the brake cylinder is 6.4 cm2. The coefficient of friction between shoe and wheel drum is 0.50. If the wheel has a radius of 34 cm, determine the frictional torque about the axle when a force of 44 N is exerted on the brake pedal.

http://img690.imageshack.us/img690/2138/screenshot20121203at907.png

Homework Equations


This I'm honestly not sure about. I initially thought that because pressure is distributed evenly throughout all parts of the fluid, it should be

F1 / A1 = F2 / A2
But as my solution shows, apparently this is not the case

The Attempt at a Solution



I did
44 / 1.8 = F2 / 6.4
F2 = 156.4 N
Tfrictional = 156.4(0.5)(0.34) = 26.6 N *m

However, all of the answer keys state to do
44(1.8/6.4),
which results in the answer 2.1 N*m
Any help here? I'm really not sure what I'm doing wrong. THanks!
 
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I agree with your result. (It would be crazy to have to push harder on the pedal than the resulting force on the brake shoe.)
 
Hmm... the problem statement vs the picture.
 
Last edited:

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