NEET 2013 Physics question
The upper half of an inclined plane of inclination is perfectly smooth while lower half is rough. A block starting from rest at the top of the plane will again come to rest at the bottom, if the coefficient of friction between the block and lower half of the plane is given by -
Answer: (3)
Solution
Let the length of the incline be . The block starts from rest and again has zero speed at the bottom, so the net work done on it over the whole length is zero (work-energy theorem). Work done by gravity over the whole length . Work done against friction acts only on the rough lower half:
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