A block of mass m₁= 4.0 kg is put on top of a block of mass m_b= 5.0 kg. To cause the top block to slip on the bottom one while the bottom one is held fixed, a horizontal force of at least 12 N must be applied to the top block. The assembly of blocks is now placed on a horizontal, frictionless table (Figure). Find the magnitudes of?

(a) The maximum horizontal force F that can be applied to the lower block so that the blocks will move together and

(b) The resulting acceleration of theblocks.