help!! Two neighbors communicate with a homemade string phone (see figure below)

Question

help!!

Two neighbors communicate with a homemade string phone (see figure below). The simple phone consists of two ends of a string (total mass of 21 g) attached to the bottom of two paper cups. The string is stretched between the two homes at a tension of 14 N over the distance of 34 m. How long does it take communication to travel on the string from one home to the other? How long would it take to communicate by yelling out the window? How long would it take to communicate over cell phones if the nearest cell tower is 6.0 km away? (Consider only the propagation time of the radio waves and assume that the call is already connected.)

Explanation / Answer

Speed of the waves in string is v = sqrt(T/mu)

Tension T = 14 N21*10^-3 kg

linear density is mu = m/l = 21*10^-3 kg/(34) =6.17*10^-4 kg /m

v = sqrt(14/(6.17*10^-4)) = 150.63 m/sec

time taken is t = d/v = 34/150.63 = 0.225 sec

B) time taken by sound waves is t = d/v = 34/343 = 0.099 sec

C) time taken by the radio waves is t = d/v = 6000/(3*10^8) = 20*10^-6 Sec

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