## College Physics (7th Edition)

a). $1.08s$ b). $1.04s$
$v=331+0.6T$ At $20^{\circ}C$, $v=331+(0.6)(20)=343m/s$ Speed of sound in steel = 4500m/s a). d= 400m Rail: $t=\frac{400}{4500}=0.09s$ Air: $t=\frac{400}{343}=1.17s$ Time lapse = $1.17-0.09=1.08s$ will elapse when the second will reach the person. b). Speed of air = 36km/hr = 10m/s Actual speed of sound = 343+10=353m/s Air: $t=\frac{400}{353}=1.13s$ Thus, time lapse = $1.13-0.09=1.04s$