He tried to get on to his feet but his head refused to cooperate so he decided to sit where he was for the time being.

cooperate 是动词，由前缀 co-（表示"共同"）和 operate（运作、操作）组成，字面意思是"共同运作"。在这里引申为"配合、协作"的意思，指头部无法配合他站起来的动作。