A small block with mass 0.0400 kg is moving in the xy -plane. the net force on the block is described by the potential-energy function u(x,y)=(5.65j/m2)x2−(3.60j/m3)y3 .what is the direction of the acceleration of the block when it is at the point x = 0.29 m , y = 0.60 m ?