Chapter 16

 2) v = lambda/T = lambda * f  ===> f = v/lambda = 0.025m/1470 (m/s) 
                                                 = 1.7 10^-5 s

14) Linear density of the string (m/L) does not change
     v_1 = sqrt(F_1/(m/L))
     v_2 = sqrt(4F_1/(m/L)=2*sqrt(F_1/(m/L)=2*v_1
    Speed is twice larger i.e., 2*300 m/s = 600 m/s

31) The wavelength   lambda = v/f = 343 m/s / (5/s)= 68.6 m
    number of wavelengths in the distance of 480 m is 480m/68.6 m = 7

77) Doppler shift:

    f'= f * (1/(1+v'/v)) = 0.86 * f

              1
    ====>  ------- = 0.86  ====> v'/v =1/0.86 -1 = 0.1628 
           1 +v'/v
          
           v' = v * 0.1628 = 343 m/s * 0.1628 = 55.8 m/s (125 miles/h)