Question

WATER HAS THE HIGHEST SPECIFIC HEAT OF ANY ORDINARY MATERIAL, WHICH MEANS THAT IT CAN HOLD A GOOD DEAL OF THERMAL ENERGY. A CUBIC FOOT OF WATER STORES ABOUT 62 BTU/F˚, WHILE 10FT3 OF WATER WILL STORE 620 BTU/F˚. ROCKS HAVE A MUCH SMALLER SPECIFIC HEAT BUT A MUCH GREATER DENSITY THAN WATER. IF THE SPECIFIC HEAT OF ROCK IS .2 BTU/LB-F˚ AND THE DENSITY IS 170 LB/FT3, HOW MANY CUBIC FEET OF ROCK ARE NECESSARY TO STORE 620 BTU/F˚?