(Solved):   2) A retaining wall against a mud slide is to be constructed by placing 0.9-m-high and \( ...

 

2) A retaining wall against a mud slide is to be constructed by placing 0.9-m-high and \( 0.3-m \)-wide rectangular concrete blocks \( \left(\rho=2700 \mathrm{~kg} / \mathrm{m}^{3}\right. \) ) side by side, as shown in Figure. The friction coefficient between the ground and the concrete blocks is \( f=0.4 \), and the density of the mud is about 1800 \( \mathrm{kg} / \mathrm{m}^{3} \). There is concern that the concrete blocks may slide or tip over the lower left edge as the mud level rises. Determine the mud height at which (a) the blocks will overcome friction and start sliding and (b) the blocks will tip over. (40 points)