Q.A sonometer wire of length $2\ \text{m}$ has a mass of $5\ \text{g}$ and is stretched with a tension of $80\ \text{N}$. Find the speed of a transverse wave on the wire.

Given: length $L=2\ \text{m}$, mass $m=5\ \text{g}=5\times10^{-3}\ \text{kg}$, tension $T=80\ \text{N}$.

Mass per unit length: $\mu = \frac{m}{L} = \frac{5\times10^{-3}}{2} = 2.5\times10^{-3}\ \text{kg m}^{-1}$

Using $v=\sqrt{T/\mu}$:

Find $\mu=m/L$ in $\text{kg m}^{-1}$, then substitute directly into $v=\sqrt{T/\mu}$.

• Forgetting to convert the mass from grams to kilograms before computing $\mu$.
• Using the wire's total mass $m$ in place of $\mu$ directly in the formula, instead of first dividing by the length.