A thermally insulated vessel contains an ideal gas of molecular mass M anda  ratio of specific heat 1.4. The vessel is moving with speed v and is suddenly brought to rest. Assuming no heat is lost to the surrounding and vessel temperature of the gas increases by :

(R = universal gas constant)

  1. \(\frac{Mv^2}{7R}\)
  2. \(\frac{Mv^2}{5R}\)
  3. \(2\frac{Mv^2}{7R}\)
  4. \(7\frac{Mv^2}{5R}\)

Answer (Detailed Solution Below)

Option 2 : \(\frac{Mv^2}{5R}\)
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JEE Main 04 April 2024 Shift 1
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90 Questions 300 Marks 180 Mins

Detailed Solution

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CONCEPT:

  • Specific heat is defined as the heat required to raise the temperature of the unit mass of a given substance by a given amount and it is written as;

           E = nCΔT     ( In short, this is the energy gain in the system)

CALCULATION:

Given: γ = 1.4

Let us take "n" moles of the gas.

The energy loss is equal to the energy gain in the system and it is written as;

Eloss = Egain -----(1)

The energy loss is written as Eloss \(\frac{1}{2}\)nMv2

and the energy gain is written as Egain = nCvΔT

From, the equation we have;

Eloss = Egain 

⇒ \(\frac{1}{2}\)nMv2 =  nCvΔT

⇒  \(\frac{1}{2}\)Mv2 =  CvΔT ----(2)

 γ = 1.4 = 7/5  (given), from this we see that it is a diatomic gas, and specific heat capacity at constant volume is written as;

Cv = 5R/2

Here equation (2) becomes,

 \(\frac{1}{2}\)Mv2 =  \(\frac{5R}{2}\)ΔT 

⇒ ΔT = \(\frac{Mv^2}{5R}\)

Hence, option 2) is the correct answer.

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