Find the condition that if box once comes to rest, it remains at rest (somewhere in between the top and bottom).
A
V20=2gsin2αAsinα
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B
V20=3gsin2αAcosα
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C
V20=2gcos2αAsinα
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D
V20=3gcos2αAsinα
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Solution
The correct option is BV20=3gsin2αAcosα The box will come to rest if final velocity becomes zero before reaching highest point. mv202=mgsinαx+∫x0Axmgcosαdx or v20=2gsinαx+Agcosαx2 it will remain at rest if the net force at that place is zero i.e., μmgcosa=mgsina or Axcosa=sina or x=sinαAcosα ∴v20=2gsina(sinαAcosα)+Agcosa(sinαAcosα)2 =3gsin2αAcosα