To solve the problem of finding the temperature \(\alpha\) at which the speed of sound becomes \(2V_0\), we must first understand how the speed of sound in air changes with temperature.
The speed of sound in air is given by the formula:
\(V = V_0 \sqrt{\frac{T}{T_0}}\)
Where,
Initially, at \(T_1 = 0^\circ C\), the speed of sound is \(V_0\).
At \(T_2 = \alpha^\circ C\), the speed of sound becomes \(2V_0\).
Given: \(V = 2V_0\),
Substitute this into the speed formula:
\(2V_0 = V_0 \sqrt{\frac{T_2}{273}}\)
Cancel \(V_0\) from both sides:
\(2 = \sqrt{\frac{T_2}{273}}\)
Square both sides to eliminate the square root:
\(4 = \frac{T_2}{273}\)
Rearrange to find \(T_2\):
\(T_2 = 4 \times 273\)
Calculating:
\(T_2 = 1092 \text{ K}\)
Convert Kelvin back to Celsius:
\(\alpha = T_2 - 273 = 1092 - 273 = 819^\circ C\)
Therefore, the correct answer is \(819^\circ C\).

Two loudspeakers (\(L_1\) and \(L_2\)) are placed with a separation of \(10 \, \text{m}\), as shown in the figure. Both speakers are fed with an audio input signal of the same frequency with constant volume. A voice recorder, initially at point \(A\), at equidistance to both loudspeakers, is moved by \(25 \, \text{m}\) along the line \(AB\) while monitoring the audio signal. The measured signal was found to undergo \(10\) cycles of minima and maxima during the movement. The frequency of the input signal is _____________ Hz.
(Speed of sound in air is \(324 \, \text{m/s}\) and \( \sqrt{5} = 2.23 \)) 