Question

Two pulses in a stretched string whose centres are initially $8cm$ apart are moving towards each other as shown in the figure. The speed of each pulse is $2cm/s$. After $2$ second, the total energy of the pulses will be

• A. zero
• B. purely kinetic
• C. purely potential
• D. partly kinetic and partly potential

Answer 1

Answer: (B)

The two pulses are moving towards each other. The speed of each pulse is $2cm/s$
$\therefore$ After $2sec$, one pulse moves to left by $4cm$ and other pulse moves to right by $4cm$.
$\therefore$ They superpose and annul the displacement of each other. The string will become straight
Hence there will be no potential energy
$\therefore$ The total energy of the pulses will be kinetic