A long aluminum rod is struck at one end. At the other end an observer close to the rod, hears the sound of the blow twice (once through air and once through the rod), with a 0.840 s interval in between. What is the length of the rod? (The speed of sound in aluminum is 6420.0 m/s.)
-
Time taken in air Ta = L/Va, in rod Tr = L/Vr
Ta - Tr = 0.84s
L(1/Va - 1/Vr) = 0.84
Assuming Va = 340 m/s ..
(1/Va - 1/Vr) = 1/340 - 1/6420 = 0.002785
L(0.00279) = 0.84 .. .. L = 0.84/0.002785 .. .. ► L = 301.6 m
Ta - Tr = 0.84s
L(1/Va - 1/Vr) = 0.84
Assuming Va = 340 m/s ..
(1/Va - 1/Vr) = 1/340 - 1/6420 = 0.002785
L(0.00279) = 0.84 .. .. L = 0.84/0.002785 .. .. ► L = 301.6 m