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blackandyello
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Homework Statement
A small wedge is placed beneath corner B of the 4000-kg block of marble.
Determine the largest angle θ for which the wedge is self-locking; that is, the
wedge will not slide out from under the block. Neglect the mass of the wedge and
the small angle between surface AB and the horizontal.
http://screensnapr.com/e/527Zk6.jpg
Homework Equations
using the FBD of the whole composite body.
summation of forces on x = 0
0.2Na - 0.2Nc = 0
summation of forces on y = 0
-39240 + Na + Nc = 0
solving, it yields = Na = 19620 Nc = 19620
The Attempt at a Solution
now, we take the fbd of just the wedge
summation of forces along x = 0
Nb cos(90-θ) -fb cos(θ) - fc = 0
summation of forces along y = 0
-Nb sin(90-θ) - fb sin(θ) + Nc = 0
dividing those 2 eqns yields:
-tan(90-θ) + tan(θ) - (Nc/fc)
then since we have Nc and Fc (using f = uN) where u = 0.2
and θ yields arounds 70 degrees which is incorrect (the book says 18.15 degrees)
thanks
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