$5\mathrm{.}5$ In a cylindrical coordinate system, a $2$mlong straight wire

carrying a current of $5$A in the positive z direction is located at

r $=4$ cm$,\text{'}=(/2,$ and $1$ m $\%$ z $\%1$ m$.$If B $=$r $0\mathrm{.}2$ cos $\text{'}($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 $\text{'}$ direction $($while maintaining

r $=4$ cm$)?$

$($c$)$ At what angle $\text{'}$ is the force a maximum?