Wave Motion 5 Question 3

3. 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 2s the total energy of the pulses will be

(2001, 2M)

(a) zero

(b) purely kinetic

(c) purely potential

(d) partly kinetic and partly potential

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Answer:

Correct Answer: 3. (b)

Solution:

  1. After two seconds both the pulses will move 4cm towards each other. So, by their superposition, the resultant displacement at every point will be zero. Therefore, total energy will be purely in the form of kinetic. Half of the particles will be moving upwards and half downwards.



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