$[2]$ Apply force $P=2kN$ to the clamp handle to pick up the object with force Q $.$ The

figure below shows the equilibrium state.

At this time, find the minimum diameter of the pin at the clamp connection part A

that is resistant to shear. However, the allowable shear stress of the pin is $10$ MPa

and the safety factor $n=1\mathrm{.}8$

$[25$ points$]$