Chapter 18, Problem 18.1QQ

To determine

The effect that happens when two pulses overlap to each other.

Answer to Problem 18.1QQ

Option (c) the string forms a straight line.

Explanation of Solution

When two pulses travel in the opposite direction then the pulses cancel each other in terms of displacement of elements of the string from equilibrium, but the string is still moving. A short time later, a string will displaced again and the pulses will have passed each other and forms a straight line.

Thus, the string forms a straight line when two pulses completely overlap on the string.

Conclusion:

If string movement is zero and pulses cancel to each other then energy associated with pulses disappeared, which is contradictory. Thus, option (a) is incorrect.

When two pulses does not travel in the opposite direction on the string then string will not move, which is not the case. Thus, option (b) is incorrect.

The string forms a straight line because pulses continues pass each other Thus, option (c) is correct.

When the two pulses overlap in equilibrium condition and after that string does not move then pulses have vanished and will not reappear, which is contradictory. Thus, option (d) is incorrect.