Figure (15-E7) shows two wave pulses at t = 0 travelling on a string in opposite directions with the same wave
speed 50 cm s−1. Sketch the shape of the string at t = 4 ms, 6 ms, 8 ms, and 12 ms.
We know that travelled distance by any classical wave follows,
So, in each case,
T=4 ms 
T=6 ms 
T=8 ms 
T=12 ms 
The sketch is given:
1