A litre of dry air at STP expands adiabatically to a volume of 3 litres. If γ=1.40, the work done by the air is (take 3^1.4=4.6555 and treat air as an ideal gas)

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(3) 90.5 J. Adiabatic work: W=(P₁V₁-P₂V₂)/(γ-1), γ-1=0.4. At STP P₁=1.013×10⁵ Pa and V₁=10⁻³ m³, so P₁V₁=101.3 J. P₂=(P₁)/(3^1.4)=(P₁)/(4.6555) and V₂=3×10⁻³ m³, so P₂V₂=(3P₁V₁)/(4.6555)=65.28 J. W=(101.3-65.28)/(0.4)=(36.02)/(0.4)=90.06 J. The printed option is 90.5 J, which is 90.06 rounded loosely.

A litre of dry air at STP expands adiabatically to a volume of 3 litres. If γ=1.40, the work done by the air is (take 3^1.4=4.6555 and treat air as an ideal gas)

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