Question No$.11$: In a thrust bearing the external and internal radii of the contact surfaces are $210$ mm and $160$ mm respectively. The total axial load is $60$ kN and coefficient of friction $=0\mathrm{.}05.$ The shaft is rotating at $380$ rpm $.$ Intensity of pressure $-$is not to exceed $350k\frac{N}{m^2}.$ Calculate:

$($i$)$ Power lost in over$-$coming the friction and;

$($ii$)$ Number of collars required for the thrust bearing.