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A bob of mas M is suspended by a massles...

A bob of mas `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 pi`

Text Solution

Verified by Experts

The correct Answer is:
`(4)`
From given condition, `v = sqrt(5gl)` From energy conservation

`(m(v/2)^(2))/2 - (mv^(2))/2 = -mgL(1-cos theta)`
`or cos theta = -7/8` The value of `theta` given in option(4) can only have a value of `theta` as computed above, so(4) is correct.
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NARAYNA-WORK , ENERGY & POWER -EXERCISE IV
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