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The velocity of sound at $15 ^\circ \mathrm{C}$ and $380 \mathrm{mm}$ pressure is 340 metres per second. If the temperature remains constant and pressure is doubled, the velocity of sound will be:
(A) 340 metres /sec
(B) 170 metres/sec
(C) 680 metres/sec
(D) None of the above

Last updated date: 18th Jun 2024
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Hint: We should know that velocity is defined as the rate change of displacement per unit time. Speed in a specific direction is also known as velocity. Velocity is equal to displacement divided by time. Speed, being a scalar quantity, is the rate at which an object covers distance. The average speed is the distance which is a scalar quantity per time ratio. On the other hand, velocity is a vector quantity; it is direction-aware. An object which moves in the negative direction has a negative velocity. If the object is slowing down then its acceleration vector is directed in the opposite direction as its motion in this case. Based on this we have to solve this question.

Complete step by step answer
We know that the velocity of sound $\mathrm{v}$ in a gas is given by Laplace formula
$\mathrm{v}=\sqrt{\gamma \mathrm{P} / \rho}$
where $, \mathrm{P}=$ pressure of gas,
$\rho=$ density of gas, $\gamma=$ ratio of specific heats at constant pressure and volume
for 1 mole of gas, $\mathrm{PV}=\mathrm{RT}$ where volume of gas, $\mathrm{V}=\mathrm{M} / \rho,(\mathrm{M}=$ mass of one mole of gas or molecular mass),
So, we have, $\mathrm{P}(\mathrm{M} / \rho)=\mathrm{RT}$
or $\mathrm{P} / \rho=\mathrm{RT} / \mathrm{M}=\mathrm{constant},$ if $\mathrm{T}$ (temperature of the gas) is constant,
Therefore, at constant temperature, ratio $\mathrm{P} / \rho$, remains constant hence velocity remains constant therefore we can say that pressure change has no effect on velocity of sound in a gas. As in the given question, temperature is constant therefore velocity of sound will also remain constant i.e. $340 \mathrm{m} / \mathrm{s}$.

So the correct answer is option A.

Note: We should know that if an object's speed or velocity is increasing at a constant rate then we say it has uniform acceleration. The rate of acceleration is constant. If a car speeds up then slows down then speeds up it doesn't have uniform acceleration. The instantaneous acceleration, or simply acceleration, is defined as the limit of the average acceleration when the interval of time considered approaches 0. It is also defined in a similar manner as the derivative of velocity with respect to time. If an object begins acceleration from rest or a standstill, its initial time is 0. If we get a negative value for acceleration, it means the object is slowing down. The acceleration of an object is its change in velocity over an increment of time. This can mean a change in the object's speed or direction. Average acceleration is the change of velocity over a period of time. Constant or uniform acceleration is when the velocity changes the same amount in every equal time period.