Critical speed of rotation, N $($in rps $-$ rotation per second$)$ of a trammel is equal to $($where$,$ g $=$ acceleration due to gravity $=9\mathrm{.}81$ m$/$sec$2$ and, r $=$ radius of trammel, metre.$)$

$(1/2).($g$/$r$)$

$(1/).($g$/$r$)$

$($g$/$r$)$

$2.($g$/$r$)$