A physics student is asked to determine the length of a long, slender, copper rod by measuring the time required for a sound pulse to travel the length of the rod. The Young's modulus of copper is 1.1 × 1011 N/m2; and its density is 8890 kg/m3. The student finds that the time for the pulse to travel from one end to the other is 1.56 × 10-3 s. How long is the rod?