A block of mass M = 1.5 kg slides between two springs, of spring constant k_l = 30 N/m and k_r = 57 N/m. The distance between the relaxed springs is d = 2.8 m. The left spring is initially compressed a maximum of d_l = 0.7 m, and the block is released from rest. The first time the block hits the right spring, it compresses it a distance d_r = 0.4 m Find the coefficient of sliding friction between the block and the surface.

μ_k =