In th efigure shown in fig. `10.33` , a bob attached with a light string of radius `R` is given as initial velocity `u=sqrt(4gR)` at the bottommost point.
(a) At what height string will slack.
(b) What is velocity of the bob just befare slacking of string.

Answer

B, C

Explanation

String will slack at height `h_(1)` , discussed in article `10.5` where,
`h_(1)=(u^(2)+gR)/(3g)=(5)/(3)R` , `(as u^(2)=4gR)`
`v=sqrt(u^(2)-2gh_(1))=sqrt(4gR-2gxx(5)/(3)R)`
`=sqrt((2)/(3)gR)`