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Wave Motion and Waves on a String — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsWave Motion and Waves on a String3 Marks
Question
Two long strings A and B, each having linear mass density 1.2 x 10-2kg/m, are stretched by different tensions 4.8N and 7.5N respectively and are kept parallel to each other with their left ends at x = 0. Wave pulses are produced on the strings at the left ends at t = 0 on string A and at t = 20ms on string B. When and where will the pulse on B overtake that on A?
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Answer

$\text{m}_\text{A}=1.2\times10^{-2}\text{kg/m},\ \text{T}_\text{A}=4.8\text{N}$

$\Rightarrow\text{v}_\text{A}=\sqrt{\frac{\text{T}}{\text{m}}}=20\text{m/s}$

$\text{m}_\text{B}=1.2\times10^{-2}\text{kg/m},\ \text{T}_\text{B}=7.5\text{N}$

$\Rightarrow\text{V}_\text{B}=\sqrt{\frac{\text{T}}{\text{m}}}=25\text{m/s}$

$\text{t}=0$ in string A

$\text{t}_1=0+20\text{ms}=20\times10^{-3}=0.02\text{sec}$

In 0.02 sec A has travelled $20\times0.02=0.4\text{mt}$

Relative speed between A and B $=25-20=5\text{m/s}$

Time taken for B for overtake A $=\frac{\text{s}}{\text{v}}=\frac{0.4}{5}=0.08\text{sec}$

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