Medium INTEGER +4 / -1 PYQ · JEE Mains 2021

A monoatomic gas of mass 4.0 u is kept in an insulated container. Container is moving with velocity 30 m/s. If container is suddenly stopped then change in temperature of the gas (R = gas constant) is ${x \over {3R}}$. Value of x is ___________.

Answer (integer) 3600

Solution

<p>To find the change in temperature of a monoatomic gas when the container it is in is suddenly stopped, we can follow these steps:</p> <p><p><strong>Relationship Between Kinetic Energy and Internal Energy Change:</strong> </p> <p>The kinetic energy lost by the container when it stops is converted into the internal energy of the gas:</p> <p>$ \Delta KE = \Delta U $</p></p> <p><p><strong>Expression for Internal Energy Change:</strong> </p> <p>The change in internal energy can be expressed in terms of the change in temperature:</p> <p>$ \Delta U = n C_v \Delta T $</p> <p>where $ n $ is the number of moles, $ C_v $ is the molar heat capacity at constant volume, and $ \Delta T $ is the change in temperature.</p></p> <p><p><strong>Using the Kinetic Energy Formula for the Change:</strong> </p> <p>For a monoatomic gas, the molar heat capacity at constant volume $ C_v $ is $\frac{3R}{2}$. Thus, we equate the kinetic energy to the change in internal energy:</p> <p>$ \frac{1}{2} m v^2 = \frac{3}{2} n R \Delta T $</p></p> <p><p><strong>Solving for $\Delta T$:</strong> </p> <p>Rearrange the equation to solve for the change in temperature:</p> <p>$ \Delta T = \frac{m v^2}{3 n R} $</p></p> <p><p><strong>Substituting Given Values:</strong> </p> <p>Here, mass $ m = 4 $ u, velocity $ v = 30 $ m/s, and the number of moles $ n = 1 $. Substitute these into the equation:</p> <p>$ \Delta T = \frac{4 \times (30)^2}{3 \times 1 \times R} $</p> <p>Simplifying:</p> <p>$ \Delta T = \frac{3600}{R} $</p></p> <p><p><strong>Relating to Given Expression:</strong> </p> <p>According to the problem, $\Delta T = \frac{x}{3R}$. Therefore, equating:</p> <p>$ \frac{x}{3R} = \frac{3600}{R} $</p></p> <p><p><strong>Solve for $x$:</strong> </p> <p>Simplifying gives:</p> <p>$ x = 3600 $</p></p> <p>Thus, the value of $x$ is 3600.</p>

About this question

Subject: Physics · Chapter: Thermodynamics · Topic: Zeroth and First Law

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