Could somebody please help me with this physics problem?

Question

 

 

The pulse travels to the right on a string whose ends at x = 0 and x = 4.60 m are both fixed in place. Imagine a reflected pulse that begins to move onto the string at an endpoint at the same time the incident pulse reaches that endpoint. The superposition of the incident and reflected pulses gives the shape of the string. When does the string first look completely flat for t > 0?

Answer 1

Sarah,

The answer should be 3.07 seconds when the string looks completely flat after t=0.

Solution: the velocity of the wave is required to be found here to calculate the total time it takes to reach the other fixed end where the string will be straight line again. To find the velocity, you can check the displacement of the tip or the center of the waves given in the graphs. Each increment or cell in the x-axis of the graph is 0.1m and when compared, the tip/ middle of the wave moved by three cells in the graph meaning 0.3 m and the time difference is 0.2 sec. Therefore, the velocity is distance/ time which is 0.3m/0.2sec= 1.3 m/sec. Now the total time to complete the whole string length is 4.6m/ 1.5(m/sec) = 3.07 seconds.