A monoatomic gas is compressed from a volume of 2   m 3 to a volume of 1   m 3 at a constant…

A monoatomic gas is compressed from a volume of 2 m3 to a volume of 1 m3 at a constant pressure of 100 N m2. Then it is heated at constant volume by supplying 150 J of energy. As a result, the internal energy of the gas
  1. Decreases by 50 J
  2. Increases by 250 J
  3. Decreases by 250 J
  4. 0 J

Solution

Isobaric process with Q=0

∴ 0=W+ΔU

∴ 0=PΔV+ΔU

∴ ΔU=-PΔV

      =-1001-2 J

      ΔU=100 J

Constant volume with Q=150 J

Q=0+ΔU

∴ ΔU2=150J

∴ ΔU=ΔU1+ΔU2

               = + 2 5 0 J

Hence, internal energy increases by 250 J

Asked in: JEE Main 2014 (19 Apr Online)

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