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Reviewed CSCA Physics question · Easy

A gas in a cylinder absorbs 600 J of heat from its surroundings while the gas expands and does 250 J of work on the piston. What is the change in internal energy of the gas?

  1. 850 J
  2. 350 J
  3. -350 J
  4. -850 J
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Correct answer

B. 350 J

Principle or equation

The first law of thermodynamics: ΔU = Q - W, where Q is heat added to the system and W is work done by the system.

Why this answer is correct

Here Q = +600 J (heat absorbed) and W = +250 J (work done by the gas). Therefore ΔU = 600 J - 250 J = 350 J. The internal energy increases by 350 J.

Example

If a gas absorbs 100 J of heat and does 40 J of work, its internal energy increases by 60 J.

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