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As shown in fig., a bob of mass m is tie...

As shown in fig., a bob of mass m is tied by a massless string whose other end portion is wound on a fly wheel (disc) of radius r and mass 2m. when released from rest the bob starts falling vertically. The time taken by the bob to descend through a height h, from the initial position, is

A

`2sqrt(h/g)`

B

`sqrt((2h)/(g))`

C

`sqrt((4h)/(3g))`

D

`sqrt((2h)/(3g))`

Text Solution

Verified by Experts

The correct Answer is:
A
T.r = `(2 mr^2)/(2) alpha`
`implies T = mralpha " " ….(i)`
`mg - T = mg = m r alpha implies r alpha = g/2 = a`
`:. h = 0 + 1/2 (g/2) .t^2 implies t = sqrt((4h)/(g)) = 2sqrt(h/g)`
.
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