The speed of a standing wave in a string is given by
[tex]v= \sqrt{ \frac{T}{\mu} } [/tex]
where T is the tension of the string and [tex]\mu= \frac{m}{L} [/tex] is the linear mass density, with m being the mass of the string and L its length. Substituting into the first formula, and using the values given by the exercise, we can find the speed of the wave
[tex]v= \sqrt{ \frac{TL}{m} }= \sqrt{ \frac{(150 N)(7.2 m)}{0.75 kg} }=37.9 m/s [/tex]
So now we can calculate how long does a pulse take to travel from one support to the other: the distance is 7.2 m, the speed is 37.9 m/s, and this is a uniform linear motion, so the time is given by
[tex]t= \frac{L}{v}= \frac{7.2 m}{37.9 m/s}=0.19 s [/tex]
