A stone of m ass m tied to the end of a string revolves in a vertical circle of radius R. The net force at the lowest and highest points of the circle d irected vertically dow nw ards are : [Choose the correct alternative]
Lowest Point (a) mg - `T_(1)`
(b) `mg + T_(1)`
(c) `mg + T_(1) - (mv_(1)^(2))//R`
(d) `mg - T_(1) - (mv_(1)^(2))//R` Highest Point `mg + T_(2)`
mg - `T_(2)`
`mg - T_(2) + (mv_(1)^(2))//R`
`mg + T_(2) + (mv_(1)^(2))/R`
`T_(1)` and denote the tension and speed at the lowest point. `T_(2)` and `v_(2)` denote corresponding values at the highest point.

Explanation

When stone is tield at end of string and whirled in circular path in vertical plane let H be highest point and L be lowest point
At point L :
Tension `T_(1)` toward centre and weigth mg is in downward direction

Resultant force acting on stone is in downward direction
Resultant force =mg = `T_(1)`
At point H : Here tensiion `T_(2) ` and weight mg
Hence option ( A) is correct .