Two pulses move in opposite directions on a string and are identical in shape except that one has positive displacements of the elements of the string and the other has negative displacements. At the moment the two pulses completely overlap on the string, what happens?
Correct answer: C. The string forms a straight line for a moment
- A. The energy associated with the pulses has disappeared
- B. The string does not move afterwards
- C. The string forms a straight line for a moment
- D. Pulses vanished and will not appear again
Explanation
When two pulses of equal amplitude but opposite in direction overlap on a string, they cancel each other out momentarily, making the string appear straight due to destructive interference. However, the energy is conserved, and the pulses continue moving in their original directions after the overlap.Option C is correct because it accurately describes the phenomenon of destructive interference resulting in a straight line momentarily. Options A, B, and D are incorrect because they either imply the loss of energy or incorrectly state that the pulses or movement cease permanently.
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About Waves
Progressive waves transfer energy through oscillations, with wavelength, frequency, amplitude and wave speed related by v = fλ; sound speed depends on the medium. Superposition produces interference and stationary waves in strings and organ pipes, while simple harmonic motion describes the oscillation itself and must be distinguished from wave propagation.
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