• # question_answer A hole is to be punched in a 15 mm thick plate having an ultimate shear strength of  3 N-$m{{m}^{-2}}.$If the allowable crushing stress in the punch is $6\,N$-$m{{m}^{-2}},$ the diameter of the smallest hole which can be punched is equal to: A) 15 mm             B) 30 mmC) 60 mm             D) 120 mm

$\pi dt\pi =\frac{\pi }{4}\,{{d}^{2}}{{\sigma }_{c}}$ $d=\frac{4t\pi }{{{\sigma }_{c}}}=\frac{4\times 15\times 3}{6}=30\,mm$