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JEE Main 2004 (AIEEE) · Friction on an Incline

Friction on an Incline question from JEE Main 2004 (AIEEE)

Q31JEE Main 2004 · AIEEEEasy

Friction on an Incline

A block rests on a rough inclined plane making an angle of 30∘30^\circ with the horizontal. The coefficient of static friction between the block and the plane is 0.8.0.8. If the frictional force on the block is 10 N,10\text{ N}, the mass of the block (in kg\text{kg}) is (take g=10 m/s2)(\text{take } g = 10\text{ m/s}^{2})

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Answer: (c)

  1. Block at rest: static friction equals the component of weight along the incline.
  2. f=mgsin⁡30∘⇒10=m(10)(0.5)f = mg\sin 30^\circ \Rightarrow 10 = m(10)(0.5)
  3. m=2 kgm = 2\text{ kg} (check: μscos⁡30∘=0.69>sin⁡30∘\mu_s\cos 30^\circ = 0.69 > \sin 30^\circ, so it can stay at rest).
  4. So the answer is (c) 2.0.
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