Solving Viscosity Problems in an Auto Lift

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Homework Help Overview

The problem involves an auto lift system where a ram slides within a cylinder filled with viscous oil. Participants are tasked with determining the viscosity of the oil and the shear stress at the surface of the inner cylinder, given specific dimensions and conditions of the system.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of the surface area of the cylinder and ram, questioning the significance of any differences. There is also an attempt to relate the force and viscosity equations to the problem context.

Discussion Status

Some participants have provided calculations for the surface areas and viscosity, while others express uncertainty about the correctness of their results. There appears to be a collaborative effort to verify calculations and clarify concepts related to the problem.

Contextual Notes

Participants mention the need for accurate calculations due to the importance of the assignment, which is tied to a class presentation and counts as a test.

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Homework Statement


An auto lift consists of a 55.56 cm diameter ram which slides concentrically in a 55.58 cm diameter
cylinder (see Figure 1). The cylinder engages a 2.8 m length of the ram at all times. The annular region
between the ram and cylinder is filled with viscous oil. The combined mass of the automobile, auto rack
and ram is 1750 kg. If the lift drops steadily at the speed of 0.25 m/s after being released, determine:
a) the viscosity of the oil, in Pa.s,
b) the shear stress at the surface of the inner cylinder.


Homework Equations



F=uA(v/y)
F=mg
t=u(du/dy)

The Attempt at a Solution



I can find the force which is the weight og ram+ram, also dy and dv. but i don't know how to find A. my friends told me that A = 2pi*2.8 put i don't think it was right because 2.8m is the length of the whole thing not diameter.
Please help me. I need to give my class a presentation about this and it counts as a test.
 
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What is the surface area of the cylinder? What is the surface area of the ram? Is the difference really significant?
 
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the surface of the cyclinder is 4.89m^2 and the surface area for the ram is also 4.89m^2. and no i don't see any huge differences between those values. and when i tried to find the viscosity it give me the value of 1.4kg/ms or 14 P. I don't know if mine is correct or not :( could you check for me please
 
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That's what I get.
 
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thank you very much !