## Essential University Physics: Volume 1 (3rd Edition)

Note, there are 10,000 pounds in 5 tons. a) We find how much energy it takes to get the stuff stored to 90 degrees F: $Q = (10,000)(.68)(5) = 34,000 \ J$ We now find how much energy it takes to melt it: $Q = (10,000)(104) =1,040,000 \ J$ We now find how much energy it takes to go to go to 60 degrees: $Q = (10,000)(.46)(30) = 138,000 \ J$ Thus, the total time is: $\Delta t = \frac{138,000+1,040,000+34,000}{20,000}=61 \ hours$ b) We now find how much of this time was at 90 degrees: $\Delta t =\frac{1,040,000}{20,000}=52 \ hours$