A phone cord is 3.50 m long. The cord has a mass of 0.200 kg. A transverse wave pulse is produced by plucking one end of the taut cord. The pulse makes four trips down and back along the cord in 0.750 s. What is the tension in the cord?

 T = 1.24 N

Explanation:

The wave velocity is given by

        v = √T /μ

Wave speed is also

     v = λ f

Let's look for the wavelength that you rinse from an oscillation

    λ = 3.5 / 4 = 0.875 m

The frequency is the time of an oscillation

    f = 4 / t

    f = 4 / 0.75 = 5.33 s⁻¹

We equal the equation is

    λ f = √T /μ  

    T = λ²  f² μ  

Linear density is

    μ  = m / L

    μ  = 0.2 / 3.5

    μ  = 0.0571 kg / m

Let's calculate

   T = 0.875²  5.33²  0.0571

   T = 1.24 N