EE cleaning Phase 2 HL floor, utilized skid steer to scoop material into skip placed on 4-wheeled cart. EE moved full skip/cart into elevator. Skip tipped dumping material in elevator, caused cart to roll back towards EE. Hit them in the chest/upper right arm, landed on ground. EE fell backwards, head contacted sheave ~10-15 ft. behind elevator, resulted in cut to back head.