Question

In the adjoining figure, two pulses in a stretched string are shown, If initially their centres are 8 cm apart and they are moving towards each other, with speed of 2cm/s, then total energy of the pulses after 2 s will be

• A. Zero
• B. Purely kinetic
• C. Purely potential
• D. Partly kinetic and partly potential

Answer 1

Answer: (B)

Purely kinetic

Given, Speed of each pulse = 2 cm/s

Time $t=2$
Therefore distance travelled by the pulse = $v\times t=2\times 2=4m$ towards each other.

On their superposition, the resultant displacement at every point will be zero.
Hence, total energy will be purely kinetic.