A block of mass $m$ slides on the wooden wedge, which in turn slides backward on the horizontal surface. The acceleration of the block with respect to the wedge is: Given $m = 8 \mathrm {~kg} , \quad M = 16 \mathrm {~kg}$ Assume all the surfaces shown in the figure to be frictionless.
(1) $\frac { 3 } { 5 } \mathrm {~g}$
(2) $\frac { 4 } { 3 } \mathrm {~g}$
(3) $\frac { 6 } { 5 } \mathrm {~g}$
(4) $\frac { 2 } { 3 } \mathrm {~g}$