In a helium-filled hall

PHYSICS · Single correct · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics

Problem

In a helium-filled hall, a sound pulse emitted at one wall returns as an echo after

0.040\,\text{s}

. The wall is

20\,\text{m}

from the source. Given

\gamma=1.67

R=8.31\,\text{J mol}^{-1}\text{K}^{-1}

and

M(\text{He})=0.004\,\text{kg mol}^{-1}

, the temperature of helium in the hall is closest to (a)

25^{\circ}\text{C}

(b)

71^{\circ}\text{C}

(c)

15^{\circ}\text{C}

(d)

48^{\circ}\text{C}