Answer
See answers.
Work Step by Step
a. The sketch is shown in the attached diagram. The pulses are added algebraically at that time.
b. The sketch is shown in the attached diagram. The pulses are added algebraically at that time.
c. When the string is straight, all of the energy is in the form of kinetic energy. There is no elastic potential energy at that moment, because every piece of the string is at its equilibrium position, but parts of the string are in motion.