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A bob of mass M is suspended by a massle...

A bob of mass M is suspended by a massless string of length L. The horizontal velocity v at position A is just sufficient to make it reach the point B. The angle `theta` at which the speed of the bob is half of that at A, satisfies

A

`theta = (pi)/4`

B

`pi/4 lt theta lt pi/2`

C

`pi/2 lt theta lt (3pi)/(4)`

D

`(3pi)/4 lt theta lt pi`

Text Solution

Verified by Experts

The correct Answer is:
D
`v = sqrt(5 gL)`
`(v/2)^2 = v^2 - 2gh implies h = L (1 - cos theta)`
Solving the three equation, we get
`cos theta = -7/8 "or" theta = cos^(-1)(-7/8) = 151^@`.
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