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In case (i) plane is smooth and in case (ii) plane is rough. If the time taken by the block in case (ii) to come down is 3 times to the time to come down in case (i) then the coefficient of friction of plane in case (ii) is?

Option: 1

\frac{1}{3}


Option: 2

\frac{2}{3}


Option: 3

\frac{3}{4}


Option: 4

\frac{1}{2}


Answers (1)

best_answer

Length covered in both cases is same so for smooth wedge s =ut + \frac{1}{2}at^2

s_1 =\frac{1}{2}at^2

s_1 =\frac{1}{2}g\sin\theta t^2\;\;\; -(I)\;\;\left[a = g\sin\theta \right ]

For rough wedge s_2 =\frac{1}{2}g(\sin\theta-\mu\cos\theta) (nt)^2\;\;\; -(II)\;\;\left[a = g(\sin\theta-\mu\cos\theta) \right ]

Now s_1 = s_2

\frac{1}{2}g\sin\theta t^2 = \frac{1}{2}g\left(\sin\theta - \mu\cos\theta\right)(nt)^2

Solving

\mu = \tan\theta\left[1-\frac{1}{n^2} \right ]

    = \frac{3}{4}\left[1-\frac{1}{3^{2}} \right ] = \frac{3}{4} \times \frac{8}{9} \Rightarrow \frac{2}{3}

Posted by

Gautam harsolia

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