$20\mathrm{.}12.$E On the "barrel of fun" amusement park ride a person sticks the wall once the barrel of diameter $d=4\mathrm{.}0m$ rotates at some minimum speed.

a$.$ If the coefficient of static friction between the woman of mass $m=65kg$ and the wall is ${}_s=0\mathrm{.}42,$ then what is that minimum speed?

b$.$ Express your answer to part $($a$)$ but now in units of rotations per minute.

HELP: $1$ rotation $=$ circumference of circle