The frequency \(f\) of vibrations of a mass \(m\) suspended from a spring of spring consant \(k\) is given…

The frequency \(f\) of vibrations of a mass \(m\) suspended from a spring of spring consant \(k\) is given by \(f=C m^{x} k^{y}\), where \(C\) is a dimensionless constant. The values of \(x\) and \(y\) are, respectively
  1. \(\frac{1}{2}, \frac{l}{2}\)
  2. \(-\frac{1}{2},-\frac{1}{2}\)
  3. \(\frac{1}{2},-\frac{1}{2}\)
  4. \(-\frac{1}{2}, \frac{1}{2}\)

Solution

$f=C m^{x} k^{3}$. Writing dimensions on both sides: $\begin{aligned} [M^{0} L^{0} T^{-1}]&=M^{x}[M L^{0} T^{-2}]^{3} \\ [M^{0} L^{0} T^{-1}]&=[M^{x+3} T^{-6}] \end{aligned}$ Comparing dimensions on both sides, we have
\(0=x+y \text { and }-1=-2 y \Rightarrow y=\frac{1}{2}, x=-\frac{1}{2}\)
Aliter. Remembering that frequency of oscillation of loaded spring is
\(f=\frac{1}{2 \pi} \sqrt{\frac{k}{m}}=\frac{1}{2 \pi}(k)^{1 / 2} m^{-1 / 2}\)
which gives \(x=-\frac{1}{2}\) and \(y=\frac{1}{2}\)

Asked in: JEE Mains - Units and Dimensions - Chapter Test

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