This paper proposes a control strategy to achieve landing motion for an underactuated planar robot. The model in this work consists of 4 links and is controlled by input-output linearization and output zeroing control. The output functions are designed based on the synchronization structure with the angular momentum about the ground contact point. This helps to control the angular transient motion until the model is stabilized and analyze the remaining zero dynamics when the output is achieved. A stable landing is accomplished by designing the stable zero dynamics. The controller is verified through numerical simulations.