The bob of a simple pendulum of length L, is displaced through `90^(@)`, from its mean position and then released. What will be the tension in the string when the bob of mass m will be its lowest position ?

Options

A. mg
B. 2 mg
C. 3 mg
D. 6 mg

Answer

C

Explanation

P.E. of the bob of the bob at A =K.E. of the bob at B
`mgL=(1)/(2) mv^(2) therefore v^(2)=2gL`
At the lowest point, a centrifugal force `(mv^(2))/(r )` also act on the bob.
`therefore` The tension in the string
`T=mg +(mv^(2))/(r )= mg+(mv^(2))/(L)`
`=mg +(m)/(L)xx2gL =3mg`