Q.
All surfaces shown in the figure are smooth. The system is released with the spring unstretched. In equilibrium, compression in the spring will be -
Let N be the normal reaction between m and M ,
Equilibrium of M Nsin45∘=kx ... (i)
Equilibrium of m in vertical direction gives Ncos45∘=mg ... (ii)
From Eqs. (i) and (ii), we get x=kmg