A stone tied to a string is rotated with a uniform speed in a vertical plane. If mass of the stone is `m`, the length of the string is `r` and linear speed of the stone is `v` when the stone is at its lowest point, then the tension in the string will be
(g= acceleration due to gravity)

Options

A. `(mv^(2))/r+mg`
B. `(mv^(2))/r-mg`
C. `(mv)/r`
D. `mg`

Answer

A

Explanation

For a stone of mass `m` and length of string `r` at the point B, weight `mg` acts vertically downwards. While tension `T_(B)` acts vertically upward. Their resultant provides the necessary centripetal force, that is
`T_(B)-mg= (mv^(2))/(r )`
`implies T_(B)=(mv^(2))/(r )+mg`
This is the tension of string at lowest point.