Question $(1)$

A helical compression spring is made of a $3-mm$ wire and has a free height of $60mm.$ The coil outer diameter is $15mm.$ The spring has $20$ active coils and $2$ inactive coils. The material constants for the wire are $A=1855$ and $m=0\mathrm{.}187.$ The shear modulus of elasticity $G=79\mathrm{.}3$ GPa.

$1-$ Find the spring constant $($stiffness$)$

$2.$ Find the shear stress produced in the spring when subjected to a compressive force of $60$ N$.$

$3-$ Determine whether the spring is solid$-$safe.