$5\mathrm{.}5$ In a cylindrical coordinate system, a $2$ m long straight wire carrying a current of $5$ A in the positive z direction is located at r $=4$ cm$,$ $=$ $/2,$ and $1$ m $$ z $1$ m$.$ PROBLEMS $275($a$)$ If B $=$ r$0\mathrm{.}2$ cos $($T$),$ what is the magnetic force acting on the wire? $($b$)$ How much work is required to rotate the wire once about the z axis in the negative direction $($while maintaining r $=4$ cm$)?($c$)$ At what angle is the force a maximum?