Pr$.-5]$ A plane stress element on a bar in uniaxial stress has a tensile stress of ${}_{}=78$MPa $($see

fig.$).$ The maximum shear stress in the bar is approximately $($show your calculation, $20\%)$:

$($A$)29$ MPa $($B$)37$ MPa $($C$)50$ MPa $($D$)59$ MPa