Suppose there is a pulley with a mass m hanging in one one side of the string an

Suppose there is a pulley with a mass m hanging in one one side of the string and the other side is attached to a vibrator by keeping the string in a horizontal position.The linear mass density of the string is 0.002 kg/m.The length of the spring between the pulley and the vibrator. is L=2.00 m.When the mass is either 16kg or 25 kg standing waves are observed; however no standing waves are observed with any mass between these values.Assume the pulley to be frictionless.What is the frequency of the vibrator?What is the largest mass for which standing waves could be observed?