Physics II / The First Law and Heat Capacities
Practice question · Numerical answer

A gas absorbs 800 J of heat while doing 300 J of work on its surroundings. Compute the change in its internal energy, in J.

Hints
  1. Heat entering is positive; work done BY the gas reduces its energy.
  2. Compute 800 - 300.
Show the answer

500 (answers within ±5 count)

Why

ΔU=Q+W=800300=500\Delta U = Q + W = 800 - 300 = 500 J. The gas keeps only what it does not spend pushing on its surroundings.

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