Two blocks of masses m and M are joined with an ideal spring of spring constant k and kept on a rough surface as shown. The spring is initially unstretched and the coefficient of friction between the blocks and the horizontal surface is u. What should be the maximum speed of the block of mass M such that the smaller block does not move?

• A. \[\mu g\sqrt{\frac{Mm}{\left( M+m \right)k}}\]
• B. \[\mu g\sqrt{\frac{\left( M+m \right)k}{Mm}}\]
• C. \[\mu g\sqrt{\frac{\left( 2M+m \right)m}{kM}}\]
• D. None of these