a) A wire 15.0 m long and having a mass of 100 g is stretched under a tension of

Question

a) A wire 15.0 m long and having a mass of 100 g is stretched under a tension of 200 N. If two disturbances, separated in time by 0.030 s, are generated one at each end of the wire, where will the disturbances meet, as measured in meters from the end where the later disturbance originated? b) A person sees a heavy stone strike concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.5 s apart in time. Which is heard first? How far away did the impact occur? Use Pconcrete = 2300 kg/m3 (density), Bconcrete = 20 x 10^9 N/m2 (bulk modulus), and the NTP speed of sound in air (300m/s).

Explanation / Answer

a)velocity of wave on string = sqrt (T/mu) = sqrt ( 200/.1/15) =173 m/s so the waves meet at equal distances from t=0.03 s time onwards so required distance = (15 - (173*0.03))/2 =4.905 m b) velocity of sound in concerete slab = sqrt (B/d) = 2948 m/s velocty of air at NTP = (Yrt/M) =333m/s 2948*t = 333*(t+1.5) t=.1910 distance apart = t * 2948 =563 m

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