Question

A coin placed on a gramophone record at `100//3` rpm flies off when it is place at a distance grater than 16 cm from the axis of rotation. If the record is rotating at `200//3`
A. 3 cm
B. 4 cm
C. 2 cm
D. 1 cm

Answer 1

Correct Answer - B
Condition for the stability of the coin is
`mu(mg)=mr omega ^(2)=mr(4 pi ^(2)n^(2))`
`therefore r_(1) n_(1)^(2)=r_(2)n_(2)^(2) therefore (r_(1))/(r_(2))=(n_(2)^(2))/(n_(1)^(2)`
`therefore (16)/(r_(2))=(200xx200)/(100xx100)=4 therefore r_(2)=4 cm `.