Slide

A uniform rod of mass M and length L is resting between a rough wall and a rough floor as shown in the figure. The coefficient of friction between any two surface is μ \mu . For angle θ \theta for which the rod is just on the verge of slipping is tan θ = __________ \tan\theta = \text{ \_\_\_\_\_\_\_\_\_\_} .

1 μ 2 μ \frac { 1-{ \mu }^{ 2 } }{ \mu } 1 μ 2 4 μ \frac { 1-{ \mu }^{ 2 } }{ 4\mu } None of these choices 1 μ 2 2 μ \frac { 1-{ \mu }^{ 2 } }{ 2\mu }

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1 solution

Refaat M. Sayed
Feb 8, 2016

Photo to know the direction of reactions..

First start with conditions of stability F x = F y = M = 0 \displaystyle\sum F_{x}= \displaystyle\sum F_{y}=\displaystyle\sum M= 0 Let's assume that reaction at end point is the rod in vertical surface is R 1 R_{1} and has distance X X from horizontal surface , friction force equal to R 1 × μ R_{1} \times \mu we will also named it as F F . And the reaction at end point of the rod at horizontal surface is R 2 R_{2} and has distance S S from the vertical surface , friction force equal to R 2 × μ R_{2}\times \mu . N o t e \color{#D61F06}{Note} that t a n θ = X S tan\theta=\frac{X}{S}
So we get from equations of equilibrium R 1 = R 2 × μ ( 1 ) R_{1}=R_{2}\times \mu(1) R 2 + R 1 × μ = M R_{2}+R_{1}\times \mu=M from ( 1 ) (1) we get R 2 = M 1 + μ 2 ( 2 ) R_{2}= \frac {M}{1+\mu^2}(2) Now we will take the Moment around point F F we get R 2 × μ × X + M × S 2 = R 2 × S R_{2}\times \mu\times X+M\times \frac{S}{2}=R_{2}\times S using ( 2 ) (2) we have X μ 1 + μ 2 + ̸ M S 2 = S 1 + μ 2 \frac{\not{M} * X * \mu }{1+\mu ^{2}} +\frac{\not{M*} S}{2} = \frac{\not{M} * S}{1+\mu ^{2}} Then dividing by S S we get X S μ 1 + μ 2 = 1 1 + μ 2 1 2 \frac{X}{S} *\frac{\mu }{1+\mu ^{2}} =\frac{1}{1+\mu ^{2}} -\frac{1}{2} Then X S = 1 μ 1 + μ 2 2 μ = 1 μ 2 2 μ \frac{X}{S} =\frac{1}{\mu } -\frac{1+\mu ^{2}}{2\mu } =\boxed {\frac{1-\mu ^{2}}{2\mu }}

thats a painful amount of latex to write .. wll done :)

Jaswinder Singh - 5 years, 4 months ago

Greatly detailed solution!

Pulkit Gupta - 5 years, 4 months ago

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Thanks. I just try to do my best

Refaat M. Sayed - 5 years, 4 months ago

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