You cast some metal of density p_m in a mold, but you are worried that there might be cavities within the casting. you measure the weight of the casting to be w, and the buoyant force when it is completely surrounded by water to be b. show that v_0=b/(p_water g) – w/(p_m g) is the total volume of any enclosed cavities. if your metal is copper, the casting's weight is 158 n, and the buoyant force is 22 n, what is the total volume of any enclosed cavities in your casting? express your answer using two significant figures. what fraction is this of the total volume of the casting? express your answer using two significant figures.