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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Specific Heat Capacities of Gases

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Specific Heat Capacities of Gases

Air ( γ = 1.4 ) is pumped to a pressure of 2 atm inside a motor...

Air (γ=1.4\gamma = 1.4) is pumped to a pressure of 2 atm2 \text{ atm} inside a motor tyre at 20^{}^{{}^{\circ}} \text{C}. If the tyre suddenly bursts, determine the temperature of the escaping air. Disregard any mixing with the surrounding atmospheric air.

Options

  1. A357 K357 \text{ K}
  2. B240 K240 \text{ K}
  3. C386 K386 \text{ K}
  4. D222 K222 \text{ K}

Correct answer

B. 240 K240 \text{ K}

Step-by-step solution

The sudden bursting of a tyre is a fast process, hence it is considered an adiabatic expansion.

For an adiabatic process, the relationship between temperature and pressure is given by:

TγP1−γ=constantT^{\gamma} P^{1-\gamma} = \text{constant}

⇒T2=T1(P2P1)γ−1γ\Rightarrow T_2 = T_1 \left( \dfrac{P_2}{P_1} \right)^{\dfrac{\gamma-1}{\gamma}}

Given:

T_1 = 20^{}^{{}^{\circ}} \text{C} = 293 \text{ K}

P1=2 atmP_1 = 2 \text{ atm}

P2=1 atmP_2 = 1 \text{ atm} (atmospheric pressure)

γ=1.4\gamma = 1.4

Substituting the values into the equation:

T2=293(12)1.4−11.4T_2 = 293 \left( \dfrac{1}{2} \right)^{\dfrac{1.4-1}{1.4}}

T2=293(12)0.41.4=293(0.5)27T_2 = 293 \left( \dfrac{1}{2} \right)^{\dfrac{0.4}{1.4}} = 293 \left( 0.5 \right)^{\dfrac{2}{7}}

Using the approximation (0.5)27≈0.8203(0.5)^{\dfrac{2}{7}} \approx 0.8203:

T2≈293×0.8203≈240 KT_2 \approx 293 \times 0.8203 \approx 240 \text{ K}
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