AFTER WAITING C SWITCH, JEEP AND 2 MANTRIP STARTED MOVING IN LINE, JEEP BOOM CAME OFF TROLLEY WIRE CAUSING IT TO STOP, BUX IMMEDIATELY FOLLOWING STOPPED AND WAS STRUCK IN REAR BY 2ND BUS WHICH FAILED TO STOP IN TIME. ALL INVOLVED EE EXITED MINE UNDER OWN POWER 3 EMPLOYEES FROM REAR ENDED BUS SOUGHT MEDICAL TREATMENT FOR BAKC PAIN. NO INJURIED REPORTED IN 2ND BUS.