12.23 To transport a series of bundles of shingles A to a roof, a contrac- tor uses a motor-driven lift consisting of a horizontal platform BC which rides on rails attached to the sides of a ladder. The lift starts from rest and initially moves with a constant acceleration a, as shown. The lift then decelerates at a constant rate a, and comes to rest at D, near the top of the ladder. Knowing that the coefficient of static friction between a bundle of shingles and the horizontal platform is 0.30, determine the largest allowable acceleration a, and the largest allowable deceleration a, if the bundle is not to slide on the platform D 4.4 m ai 650 TATO B 0.8 m Fig. P12.23