A bob of mass `m` is attached at one end of a string of length `l` other end of the string is fixed at point `O`. Bob is rotating in a circular path of radius `l` in horizontal plane about `O` with constant speed `v`, as shown in the figure. The average force exterted by string on the bob during its `:-`

`(A)` half revolution will be `(mv^(2))/(pil)`
`(B)` half revolution will be `(2mv^(2))/(pil)`
`(C)` one fourth revolution will be `(sqrt2mv^(2))/(pil)`
`(D)` one revolution will be zero
Select correct alternative `:-`

Options

A. Only (A) and (D)
B. Only (A), (C) and (D)
C. Only (B) and (D)
D. Only (B), (C) and (D)

Answer

C