FLT ATTENDANT WAS INJURED BY UNSECURED BEVERAGE CART DURING UNEXPECTED TURB.

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FLT WAS VMC AT 14000 FT ON HDG TO AVOID WX (SMALL LINE CUMULO NIMBUS) WE WERE SWITCHED FROM DEP CTL TO CTR FREQ. DUE TO CONGESTION ON FREQ TOOK LONG TIME TO CHK ON AND REQUEST HDG TO GET S OF LINE TO PROCEED TO DEST. WE WERE GIVEN CLB TO FL230 AND HDG TO AVOID WX. DURING CLB AND TURN WITH RADAR ON WE CLIPPED THE TOP OF A SMALL CLOUD (THAT SHOWED NO RETURN ON RADAR) AT ABOUT 15000 FT. WE ENCOUNTERED LIGHT TO MODERATE CHOP FOR ABOUT 10-15 SECONDS. PRIOR TO ENTERING CLOUD I TURNED ON SEAT BELT AND ADVISED 'A' LINE FLT ATTENDANT TO BE SEATED. WITHIN 45 SECONDS TO 1 MIN; WE ENCOUNTERED BRIEF TURB. FLT ATTENDANT IN AFT GALLEY WAS IN PROCESS OF RETURNING TO HER SEAT WHEN BEVERAGE CART SLID DURING TURB AND PINNED HER TO AFT GALLEY BRUISING HER L ANKLE. WHEN GIVEN THE HDG CHANGE IT APPEARED WE WOULD BE IN THE CLR AND SMOOTH THE ENTIRE DEV; BUT AS WE CLRED AN ECHO RETURN CLOUD WE WERE NOT CLBING FAST ENOUGH TO TOP SMALL (NO ECHO RETURN) CLOUDS. POSSIBLE FACTORS: AUTOPLT DOES NOT RESPOND AS FAST NOR TURN AS STEEP AS HAND FLOWN. THE FO HAD REDUCED SPD TO INCREASE CLB RATE PRIOR TO ENCOUNTER.