A bob hangs from a rigid support by an inextensible string of length ℓ. If it is displaced through a distance ℓ (from the lowest position) keeping the string straight, & then released. The speed of the bob at the lowest position is:
A
√gℓ
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B
√3gℓ
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C
√2gℓ
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D
√5gℓ
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Solution
The correct option is B√gℓ Distance= l change in height= lcos60=l/2
From energy conservation, PE at max height= KE at lowest point= mgl/2=mv2/2 v=√gl