What is the minimum acceleration with which bar A (Fig) should be shifted horizontally to keep bodies

Question:

What is the minimum acceleration with which bar A (Fig) should be shifted horizontally to keep bodies 1 and 2 stationary relative to the bar? The masses of the bodies are equal, and the coefficient of friction between the bar and the bodies is equal to k. The masses of the pulley and the threads are negligible, the friction in the pulley is absent.

1 A