Physics Help Forum Simple Viscosity Problem

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 Sep 3rd 2011, 10:57 PM #1 Junior Member   Join Date: Sep 2011 Posts: 3 Simple Viscosity Problem A 10-kg block slides down a smooth inclined surface. Determine the terminal velocity of the block if the 0.1-mm gap between the block and the surface contains SAE 30 oil at 60 °F. Assume the velocity distribution in the gap is linear, and the area of the block in contact with the oil is 0.1 m^2. (the diagram shows a slope downward 20 degrees from the horizontal) ---- What I did: T = 60 F = 15.56 C Looked up viscosity of SAE 30 oil at 15.56 C: mu = 0.8 N*s/m^2 h (height) = 0.1 mm = 1 * 10^-4 m tau = F/A = mu * dv/dy F = sin theta * mg Rearranging with assumption that dv/dy is constant (linear velocity gradient mentioned in problem): velocity = (tau * h)/mu = (sin (theta) * mgh)/(A * mu) = (sin (20*pi/180)*10*9.8*10^-4)/(0.1*0.8) = 0.0419 m/s The official textbook answer is 0.0883 m/s. How do I get the correct answer? EDIT: Converted this post from LaTeX to text. Last edited by pramoda; Sep 4th 2011 at 09:09 AM. Reason: Converted this post from LaTeX to text.
 Sep 3rd 2011, 10:57 PM #2 Junior Member   Join Date: Sep 2011 Posts: 3 I'm seeing: [LaTeX Error: Can't write to directory] Is this board broken? Can I post basic LaTeX?
 Sep 4th 2011, 03:01 AM #3 Physics Team     Join Date: Jun 2010 Location: Mauritius Posts: 609 I don't know about how to solve your problem, but for the LaTeX part, no, there is no LaTeX here. You might however generate a picture from here then copy/paste the link to the picture which appears. The only problem is that we are restricted to 6 images per post. You might hence want to put several equations in the same image. __________________ Jerry (Got my results!) It is easier to protect your feet with slippers than to cover the earth with carpet. No one can go back and change a bad beginning; but anyone can start now and create a successful ending. If a problem can be solved, no need to worry about it. If it cannot be solved what is the use of worrying?

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### simple problems on terminal velocity using viscosity of block

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