Question

What is the speed of sound in air at standard temperature and pressure? Given the mass of 1 mole of air is 29.0 × 10^-3 kg.

• A. 330.94 m s^-1
• B. 187.6 m s^-1
• C. 324.5 m s^-1
• D. 246.2 m s^-1

Answer 1

Answer: (A)

At N.T.P., P = 1.013 × 10⁵ N m^-2
Volume of air, V = 22400 cm³ = 2.24 × 10^-2 m³
Mass of 1 mole of air, M = 29.0 × 10^-3 kg
Therefore, density of air at N.T.P.,
$\text{ρ}=\frac{\text{M}}{\text{V}}=\frac{\text{29.0}\times {\text{10}}^{-3}}{\text{2.24}\times {\text{10}}^{-2}}={\text{1.295 kg m}}^{-3}$
Now, $v=\sqrt{\frac{\gamma P}{\rho }}=\sqrt{\frac{1.4\times 1.013\times 10^5}{1.295}}$
$={\text{330.94 m s}}^{-1}$