Fred strikes a steel (γ = 20x1010 and ρ = 7.8x103 kg/m3) train rail with a hammer at a frequency of 2.50Hz and Wilma puts her ear to the rail 1.0 km away.
a) How long after the first strike does Wilma hears the sound?
b) What is the time interval between the successive sound pulses she hears?